I remember reading a commenter on Newsarama's message boards (admittedly, hardly the bastion of intelligent comic thought) say that he hated the idea of, say, the Joker being depicted with a sympathetic origin because "I don't want to feel bad when the Joker gets beaten up."

I'm fairly certain that the people who argue for the "bad is bad" mentality are a bit more intelligent than that, but still, that even one person could think that's the way it works still boggles my mind.