Of course it isn't like he was possessed. But I keep saying this how would any of them act without any moral compass. Not just much of one, but literally none. You have a goal, you do anything and everything to get meet that goal. Any of them would do that. Dean in hell still had his soul (sure it took years for him to break), but it was his soul put through the meat grinder. And no what unlike Sam he actually asked for it. Sam made a choice to go to the deepest darkest pit in hell (and that was all him), but he had absolutely no say in being brought back in the condition he was in. None.
Even in our legal system, if you knowingly take something to impair your judgment you can beheld legally accountable. But how does the law treat people who were drugged without their knowledge or consent?
One of the things I liked so much about last week's episode is Sam getting Dean to admit that if it was him he would feel guilt and the need to make amends.
The funny thing is that Sam actually acts more like the Angels then anyone else. As Demons feel (apparently) quite gleeful in deliberately inflicting pain. While angels just do what they have to to reach their goals.
I find it interesting that the one of the biggest "What the Hell" is wrong with my bother moments is when he like Castiel is quite willing to torture a child.