If Show went with it, explored the ways in which they didn't care as much about humans (see Privilege), that could be interesting, if chilling. But no, just seems to have gotten bored with it.

I'll admit, I have a HUGE thing for dark!Winchesters, and especially so in recent seasons because of episodes like "Slash Fiction", and just the fact that the Winchesters are so messed up now. I would find the show a LOT more interesting if it was taking us down Sam & Dean's journey towards psychopathy. But that's probably something best explored in fic LOL.