Either he's just...empty, nothing more than a human gone machine-like, or he's so freaking on emotional lockdown that this is all he'll permit himself.
I'm hoping (and guessing) it's the latter. He seems to be really detached from all emotions, and it seems to be a deliberate choice to some point (like picking up a hooker, because he's obviously doing that because it's all about sex and not about feelings with a hooker).

I was wondering the same thing about the torturing scene. Sam and Castiel both were okay with it, or at least saw it as the only solution to their problem. (but knowing fandom, they're just gonna hate Sam for it...).