Last night's episode of Supernatural was basically a standard issue "can monsters stop being evil" episode, something the show has done several times now. But this time around, there was an added subtext, because of everything that Dean just went through. Spoilers ahead...
Basically, this was Dean's first episode back as a human (tempted to put that in quotation marks) after having been a demon for a few episodes. And the story of Kate the werewolf girl (from the "found footage" episode a while back) serves as a pretty decent counterpoint to the Sam/Dean situation. The Winchesters spared Kate because she promised not to kill anyone — and she's kept her promise, but she turned her sister into a werewolf, and her sister is on a murder spree. So Sam and Dean basically have to convince Kate that her sister has gone too far into monsterdom and can't be redeemed.
This is somewhat explicitly contrasted with the boys' situation, in which Sam went to crazy, extreme lengths to "save" Dean from being a demon. Something Dean doesn't hesitate to rub Sam's face in — most notably, Sam talked a shlub named Lester into selling his soul, and then Demon Dean killed Lester, which is sort of Sam's fault. Why is it not okay for Kate to go to crazy lengths to save her sister, but it's OK for Sam to go off the rails for Dean?
There's no good answer to that question, without getting into the differences between demons and werewolves, or the fact that the boys are the stars of this show and Kate is a day-player.
But the real question is — what's going on with Dean? He has one scene where he expresses a bit of remorse for the things he did as a demon, and he does finally thank Sam for bringing him back from demonhood. But he mostly acts like a megadick in this episode. He's actually acting like Sam is the one who should be struggling with remorse for demonic acts. (The 9000 times Dean had to save Sam, I feel like Dean did way worse.)
So what's this about? A few options:
1) Dean is still part demon and is screwing with Sam.
2) Dean feels so traumatized and guilty, he can't deal with it, so he's putting up a devil-may-care front
3) Dean doesn't really blame himself for any acts committed while he was a demon, but he genuinely thinks Sam went too far. Maybe he also feels bad that Sam did all that for his sake.
4) Dean has finally lost his shit and is just pretending to be functional at this point.
I'm guessing it's probably all of the above — but I guess we'll find out around the midseason break. At least Dean's stone-cold move of convincing Kate there's a new "cure" for werewolfism was kind of badass.