Who is Samuel Campbell, the man we love to hate? Many cheered when he died, some wanted to dance on his grave.  Who is this man who claims to act for family but betrays his kin?  Is there a way to understand what he did?
Let see.

In the Beginning: Who is Samuel Campbell?
We meet Samuel Campbell in the past. Dean has just been transported back to when Mary was “a babe” and living at her parents´ house.  Samuel then is a hunter, a patriarch and a family man. He seems quite settled in this life, a hunter’s life, but still a normal family life – as normal as a hunter’s family life can be.
When Dean turns up, Samuel is initially suspicious of him, but doesn’t turn him away, in the end, he easily gives in to his wife’s insistence they invite their fellow hunter in.  His wife, Deanna, a warm-hearted, open and intelligent woman, appears sincerely fond of him. They struck me as one of those old couples, married for ages, used to each other’s quirks and peculiarities, loving the other all the more for it.
And then there is Mary of course, who suffers from her father’s protectiveness, who wants to be independent, and free of the hunters´ lifestyle.  It’s obvious Samuel loves Mary, but can’t handle setting her free. And he does not want to lose her to another man who is not even a hunter.  Or to another hunter, for that matter.
Poor John, whom Samuel dislikes, he never had a chance, he couldn’t win. His only crime was to have won Mary’s heart, thus luring her away from Samuel’s protection, the only thing that could ensure her safety and well-being, in Samuel’s eyes. 
And Mary? Well, she had issues with her father, the same way any daughter or son trying to free themselves from an overprotective parent would.  Had Azazel not turned up, she would have left with John, set up her own life, things would have been awkward for a while, and then they’d have made peace.
All in all, their family life struck me as bumpy, but close. Those people may not have agreed on everything, but they clearly cared for each other.  And then it was all destroyed in a heart-beat.  Samuel died, and when he came back from the dead, he found what he loved destroyed, and he broke.
Samuel Descending
We still know nothing of Samuel and Sam returning from their respective afterlives, Crowley, Sam, Samuel, they all could have been lying or telling the truth for all we know.  Samuel claims he had been pulled from heaven, maybe that’s true, maybe not.  It doesn’t really matter, because wherever he came from, here, on earth, in this day and age, he is clearly lost.  When we see him again, in "Exile on Main Street," he is again what he was before: a hunter, a patriarch and a family man.  Or he is trying to be and it’s hard.
He is out of his time, for one thing, almost 40 years have passed in a moment for him.  Assuming he doesn’t remember Heaven (according to the angels, people will lose that memory), the last thing he knows is maybe feeling Azazel possessing him, and dying, and now he finds himself stranded in a place and time he knows nothing about.  There was Crowley, I suppose, and then Sam, SoullessSam, not the most empathetic of people, not who’d you want around if you needed support, somebody to help you through difficult times.
And difficult it must have been. He finds out, probably quite fast, how much time has passed and that not only has Deanna died with him, but his daughter, his beloved Mary, is dead and gone as well. Maybe Sam tells him, or Crowley, or he finds out for himself.  Either way, it must have crushed him. Everything is gone, his life, everything he used to have and be just disappeared.
Easy prey for Crowley then, I suppose, and the deal is made.  It probably didn’t seem so bad at first, he would still hunt monsters, no personal price involved, and Mary as the great prize. He did not realize that, ironically, the price was maybe still his soul.  And so he gets working, seeking out his kin first, I imagine, building both a family and a team to hunt with, and he starts to settle in.  It’s a shadow of what he used to have, and his wounds are too deep to heal, but he gets by and he has one thing that keeps him going: 
When all this is done, he’ll get Mary back, he’ll get his true life back.
He spends some time with Sam, getting to know his younger grandson, or thinking he is. He is clearly uncomfortable with the more ruthless things SoullessSam does, he still cares. All the same he goes along with them because he needs him, for his very own greater good, for getting Mary back.
However, letting these things happen and doing nothing about them, I think, helped pave the way for worse things to come: It killed his compassion little by little, made him numb to the suffering he was allowing, and it shed an unforgiving light for him onto Mary’s sons, creating a gap from the start.
Things weren’t all bad. Gwen, who is with him till the very end, her end, unfortunately, seems to like him and think quite highly of him. Why else would she be so shocked at what she hears from Dean? She clearly had a different picture of him.  It’s also clear he cares about her, maybe just to fill a little of the spot that Mary used have, but still.  

They work well, he is obviously a good and extremely knowledgeable hunter, and he has built a good team, and they seem pleasant enough as well.  Sam is with him, too, strangely mirroring Samuel’s own hollowness. And something is not quite right. - The family is there, but the heart is missing.
Then Dean arrives and he senses it immediately: Something is off.  And things go downhill from there.  Dean’s refusal to accept the façade as the real thing causes the first cracks, until it all finally crumbles.  It ends with Samuel’s betrayal of his grandsons, open war, and finally Sam killing Samuel in self-defence.
What would Mary say?
When Sam feels guilty for shooting Samuel, Dean tries to comfort him: “You know what I think Mom would say? She'd say just 'cause you're blood doesn't make you family. You got to earn that.“

Would she really say that?  She may think that way, yes. Blood doesn’t make you family, it’s what you do that counts.  And she would hate Samuel’s betrayal of her sons. 
Would he cease to be her father to her, though?  After all, he is true family, he has earned it with her.   We saw it “in the beginning”: They had a bond, quite obviously, and it was loving. They had issues, but she knew herself loved by him, and she knew that he meant well. And I daresay she loved him as well, not as desperately, not as protectively but love him she did, I think.
And even if he lost that love because of what he did, the love, the connection was once present.   It is my belief that when someone is close to another person, they never lose that again, not completely, no matter what happens and even when it seems that it has disappeared. A small part, a trace of that bond will remain.
So even if she hated what he did, even if she hated him for what he did, would she want him executed in cold anger? Would she want him to die such a miserable death and then say: “Good riddance?”  And would she want her own sons to do the deed? She was a hunter, remember, she knows how heavily killing weighs upon the soul.  How could she want that for her sons?
She may never talk to him again, and she may not forgive him, but she wouldn’t have him put down like a rabid dog either, and she certainly wouldn’t applaud her sons for ending his life, if not for his sake, then for theirs.
Like grandfather, like grandson?
Sam to Dean, in Two and a Half Men, on Samuel: “He is actually a lot like you.”  He sold out his grandsons. How can he be like Dean?  Well, let’s have a look.
Dean is a family man, protective of those he loves.  Samuel, as well, is a family man, and protective. We saw that “In the Beginning.” 
We also saw how he was wary at first, slow to trust, but willing to change his mind and work together.  Dean would have acted pretty much the same way, I think.
We know Dean’s sarcasm, and his rough and tough exterior hiding a soft core and a compassionate heart. We have seen bits and pieces of Samuel’s sarcasm and wry humour as well:
“Come right on in,” when they barge into his room in "Family Matters"
“Well, bring marshmallows. Already on the pyre,” when Dean wants to “pay his last respects” to the presumably dead Alpha vampire.

“Can I help you?” when he finds them searching his desk in “Caged Heat”
“Congrats. It’s a boy, sometimes,” while handing Christian the shapeshifter-baby
“A softball team? I got no clue,” on what he thinks the Alpha shapeshifter is planning for the babies.
“Would’ve asked him to stick around for a beer,” upon “scrawny” Castiel leaving them in "Family Matters."
We can only guess at the soft core and the compassionate heart, but there are hints “In the Beginning” and in “Unforgiven.”  I also think that his offer to raise the shapeshifter baby in their family came without an afterthought.
We further know Dean’s penchant for bravado, under pressure, his refusal to bow in adverse situations, and his stubborn pride.  There was a lot of that too, in Samuel, especially when confronted with his deal and their repercussions, and last not least in his ill-advised attitude in “And Then There Were None,” where he reminded me more of a petulant and sassy teen than a grown man. 
And, most importantly of all, there’s family and what it means.  From what I have seen I would venture to say that it means precisely the same for both of them; someone to love and care for, to protect, someone who needs to be around, taking precedence over just about everything and everybody.
Dean, above all had and has Sam. Samuel, above all, had Mary.  And when they lost their loved one, as Samuel correctly pointed out, and as Dean did not deny, they both did basically the same thing to get them back - They turned to a demon and were willing to deal. And damn the consequences.
When Dean brought Sam back, he had refused to help Bobby, with Sam gone, he was ok with the world ending, he didn’t care.  We all remember Dean’s incredulous  ”More important than Sam?!” in Weekend at Bobby’s.  That pretty much says it all. Sam is not everything, but nothing and no one comes before him.  Dean may no longer pay any price for Sam’s sake, he has learned that lesson, but Sam’s well-being is still central in his world.
And Samuel? Well he had Deanna, and he had Mary, and Mary is the one he can’t and won’t live without. She is his reason for doing things.  He hadn’t intended to sell out his grandsons, but when they went after Crowley, they became a threat to his big prize, to his light in the dark, in the distance, that he thought he was walking towards: Mary.
And last not least, ironically, there is a similarity even in their conflict.  At the very core of this issue, they did precisely the same thing, rejecting their own kin, claiming the other had not earned the right to be considered family, thus ignoring and hurting the true family bond the other had created with Mary.

What was and what could have been
Dean and Samuel aren’t so different after all, their focus in life is similar, they are kin and they both hold family dear. They even love the same person.  How did they end up as mortal enemies? How did it come to this?
I think the main issue here was trust.  Hunters don´t trust easily. Their world is full of nasty surprises and their survival depends on their ability to know who to trust.
Family – for those that still have one - is their haven, here they are safe, here they have each other’s back. They can trust, and they are trusted.  When Dean found himself unable to forgive Sam in “Sympathy for the Devil,” Sam accepted that. What crushed him, as we saw, was to hear Dean say that he no longer trusted him.  This came as close to cutting him out as Dean would ever get. Love was a given, but withdrawing his trust was what really hurt.  

And when the turning point in their relationship came in “Point of No Return,” it was about trust as well, Sam trusting Dean to do the right thing, and Dean needing to live up to that trust, and then trusting in return.  Love may be the foundation of their relationship, but trust is the wall to keep them safe.
When Samuel was brought back to earth, he was traumatized, he had been ripped from his family, he had been robbed of his haven, he had no one to trust, and no one who trusted him.  One of the first things he did, it seems was to try and make new connections, surround himself with kin, people of his own blood that may have grown into family.  He desperately needed people, I think, and his desire to have them close was genuine.
Why didn’t it work out then?  Because it was built on a lie. His desire for family may have been sincere, but his ultimate goal was to bring Mary back, and that took precedence over everything else, it seems.  The fact that there was a demon and a man without a soul among his family members wasn’t helping either, I’m sure.

So while some of it may have been genuine, like his concern for Gwen and her acceptance of him, some of it resembled a Potemkin village.  It lacked heart. There may have been affection, but there couldn’t really be trust, because they were living a lie, Samuel’s lie, and they must have sensed it.
When Dean entered the picture, he immediately picked up on it, and rejected Samuel quite vehemently, from the start – with some of the vehemence probably coming from his unease about Sam.  His instincts were kicking in, he felt that Samuel could not be trusted, and he was right.  Samuel wasn’t all scheming though. He was also a lonely man, still traumatized, still longing for connection, but unable to obtain it since he was still living his lie, working for Crowley.  That didn’t make him long any less though. He wanted Dean to trust him, not just to get him to cooperate, I think he truly wanted to be accepted by him, and it hurt him to have Dean reject him so vehemently.  
Dean was acting on his instincts, but that didn’t make the rejection any less painful for Samuel.  Have you ever witnessed a liar being hurt in his feelings because no one believes them? It makes no sense that they would expect to be believed, but they are genuinely and truly hurt when they experience that rejection. I think that the same thing happened here.
Samuel knew he had no right to expect trust since he was deceiving everybody, but a part of him still wished for that trust and was hurt when it was refused.
“Why can´t you give me an inch of trust, Dean?” ("Two and A Half Men")

He made repeated attempts to win Dean over, but Dean isn’t easily convinced, especially when things are clearly not right. He’s being a hunter through and through here, no leap of faith until he knows exactly where he’ll land.
While Dean cannot be blamed for not trusting Samuel, at all, I still think that it is in part what led to Samuel becoming more antagonistic towards them.  The breaking point came first in “Family Matters,” when his scheme is discovered, and Dean just barely keeps Sam from killing Samuel then and there.
If this gave Samuel hope that Dean would understand, it was crushed in “Caged Heat.”  I think that part of the reason why Samuel fought so hard for Dean’s acceptance was not only the fact that he was Mary’s son, but also that if anyone could understand and maybe even share his desire to bring Mary back, it would be Dean (Sam didn’t count, for obvious reasons).
When Samuel confesses to Dean, showing him Mary’s picture, it’s clearly in the hope that Dean will understand. He is appealing to Dean here, trying to get him on his side, baring his heart to him.  Dean is very sincere, very open in his reaction. This is the closest they ever get to each other, they could have made a true connection there, and they almost do.
In the end, it’s Samuel who turns away, this time it is he who refuses to trust, his desire for what could be stronger than his wish to embrace what is there. If Dean could have Sam back from the dead, why should he not have Mary?
They could have turned things around, then and there, but Samuel, it seems, couldn’t find the strength to build a new true family in this current life, to have trust in Dean. Instead, he chooses to hang onto the picture of the family that had been.
He can’t give up Mary, he can’t muster the strength, and now her sons are forcing him to choose.  They are threatening to take her away forever by going after Crowley.  He can’t have that, and there is only one solution that he sees.  How does he justify it?   The same way that Dean later did when trying to kill him, by telling himself that they may be blood but not family.  If they were family, he reasons, they would care about Mary and would want to bring her back as well.  I think he has really convinced himself this is the truth.
He even comes to Dean after he has betrayed them, in a last effort to make him see. Does he want forgiveness? Not really. He wants to hear that he is right, so he can go on believing it. He does not want to see how warped his sense of family has become. Dean, understandably, does not give his blessing, and cuts the last remaining connection by threatening Samuel.  They are now mortal enemies, on opposite sides of the same conviction.  They see the other as a traitor to true family, and a threat.
When they unexpectedly meet again in “And Then There Were None,” things quickly go from very bad to worse.
Dean is all set on killing Samuel, grandfather or not. We know how angry Dean can get, but this goes far beyond anything we have ever seen from him.  Was it because, even though he couldn’t trust him – yet – he still considered Samuel potential family, so his betrayal went deeper than someone else’s would have?
Was there also some lingering anger at himself for his own choices, his own deal, now mirrored in Samuel’s actions to a certain extent, and at the same time the need to emphasize the difference between them, the things he would not have done, even to get Sam back?  Was part of it fear, the need to eliminate a potential danger to himself and, more importantly, to Sam?
And would he really have killed him? Or was there still a way out?  I believe things would have taken another turn if Samuel’s attitude had been different.  From the start he is both belligerent and cocky.
He has not been well, I’m sure. Crowley is gone, and with him his last hope of seeing Mary again.  He has betrayed his grandsons, fed Mary’s sons to ghouls – and as much as he is lying to himself, deep down he does know he did wrong.  The rest of his family is dead and gone, only Gwen is left. He seems to care about her, but it’s not enough.  When confronted with the brothers´ hostile attitude, he closes himself off completely, all bravado, stubborn pride and pure show.  Had he appealed to them, had he been open, it might have made a difference. I think it would have.  It could not have repaired things, far from it. It could still have re-established some sort of connection, not family, but a mutual understanding that they were still blood, and still had Mary, and go from there.
Had they had a little more time, maybe he would have relented, maybe they would have found a way out.  Or not.  We will never find out.  Gwen dies, and the rest of Samuel’s life with her. Shortly afterwards he is possessed, becomes more hostile during possession and ultimately pushes his own grandson into killing him.  An abrupt and shocking ending to a tragic family story.
The episode ends with Dean offering absolution to the members of his family at Rufus´ grave.  He talks about how life is too short to bear grudges. His focus is on the grudge weighing a person down, tainting their own lives.  With this, he touches upon a very basic aspect of forgiveness - It not only frees the offender from their guilt, just as importantly, it also relieves the injured from their resentment, thus lightening their lives.
They had just buried or were about to bury Gwen and Samuel as well.  Did what Dean said refer to Samuel, too? Was he included in Dean’s absolution?  I think not, not yet.
I thought I heard a hint of regret over what had happened, an admission that things should and could have gone differently.  They are not ready to forgive Samuel yet, but they will be.  What Dean says about forgiveness not only works for family, it applies to everybody and all offences, and they seem just one step away from understanding that.  

Lingering anger taints the soul, always.  Forgiving Samuel will free them, and help them grow again.  I’m hoping for them, at some point, to look with compassion upon the broken shell their grandfather had become, and with love upon the man who loved Mary.