"People can change. There is reason for hope."
Supernatural is told from Dean’s point of view. We see Sam through Dean’s eyes, we see how Sam’s actions affect Dean’s emotions, etc. When Sam leaves for Stanford, we learn that it was “the worst day of [Dean’s] life,” and that Dean thinks family doesn’t mean as much to Sam as it does to him. When Sam drinks demon blood and chooses to side with Ruby instead of listening to Dean, all we see is how betrayed and angry Dean feels. We see only glimpses of Sam’s journey in flashbacks or in what he chooses to tell Dean.
I think all of this makes it easy for fans to think Sam doesn’t love Dean as much as Dean loves him, or that Sam is selfish or even downright evil. And that seriously breaks my heart, because I think it’s so fucking far from the truth that “unfair” doesn’t even begin to cover it.
Sam has had to struggle against forces outside of his control since birth. He was doomed to become one of Azazel’s Special Children before he was even born, ever since Mary made the deal that sealed his fate. And ever since then, he’s been trying to fight the life that’s been chosen for him, trying to gain back the control that’s been taken from him.
The worst thing you can do to someone is take away their freedom of choice. Sam fought for his right to choose, despite all the forces of Heaven and Hell trying to take that away from him. He chose to break free from the life he was raised in and try to find happiness in something safe and normal. He chose to develop his powers in order to kill Lilith and avenge his brother. He chose to say “Yes” to Lucifer because it was the only way to put him back in the Pit. Regardless of whether or not you think these choices were right or wrong, Sam made them out of a desire to do good. And then he accepted the consequences that came with all of these choices.
Sam’s guilt is huge, but it doesn’t cripple him. He says “I did it. I started the apocalypse.” and then he goes right on fighting. It would be so easy for him to blame others for his misfortunes. He never asked for demon blood — that was his mother’s curse. He never asked to be raised into the life of a hunter — that was his father’s vendetta. He never knew Lilith’s death would break the final seal — and didn’t Dean break the first? Didn’t Castiel release him from the panic room knowing full well what would happen?
But Sam never says any of that, never points the finger at anyone else. He blames himself for the deaths of so many, from his girlfriend Jessica to that one civilian he couldn’t save. He begs Dean to kill him if he starts to turn into something he’s not. He accepts full responsibility for starting the apocalypse, even though he was being manipulated by demons and angels alike. And even now, he feels responsible for the things he did when he was soulless and literally had no control over his actions.
And let’s not forget: Sam willingly faced an eternity in the deepest pits of Hell in order to save the world, and to save his brother. (Same thing, really.)
Sam has had to toughen up over the years. Dean used to tease him for being too soft, for still dreaming of a normal life, for praying every night. Sam’s gotten older now, is a stronger hunter than Dean in some respects. He’s given up any ideas of getting out of the hunting lifestyle and settling down. But there’s still something so incredibly vulnerable about him, about his heartbreaking desire to be good. And throughout everything, everything he’s been through, Sam never gives up hope.