Heroes are boring. It's an inescapable truth. "Ooh, look at us, we're following the rules." Boring! Villains are so much cooler. And they get to kill people, all the time, which is awesome. Sometimes, when people get tired of somebody doing the same things over and over again, it's okay to just make them inexplicably a twisted psychopath bent on complete evil regardless of any previously existing characterizations. These characters get sent to Hero rehab where they get over themselves, get the sticks out of their asses and learn to have some fun.
Contrast with: Villain rehab
- Green Lantern was pissed off when his city got blown up, and his loved ones were killed. Solution? Kill all of his other friends! He slaughtered the entire rest of the Green Lantern Corps, and then tried to blow up time. He's back to being a goody two-shoes now, though.
- Mary Marvel, the most pure and incorruptible girl in the universe, had no problem turning evil at the drop of a hat.
- Batgirl had several years of intensive work chronicling her psychological reasons for being a hero. But then she had to go through... daddy issues!? That was too much for her otherwise unbreakable mind, and she had to start murdering as many people as she could and hanging out with ninjas.
- Solomon Grundy was good for a couple of years when he joined Infinity, Inc.. But really, who wants to read about a zombie that isn't killing people?
- Two-Face was regular Harvey Dent for awhile after Hush fixed him up, but being framed by the Tally Man and Great White Shark drove him over the edge. And what was it that made him so crazy? The idea that Batman would harbor any slight distrust for him, after several months when he was specifically not the crazy homicidal psychopath he had been for the rest of his life!
- Jason Todd used to be a goody two shoes Robin, as well. Then the Joker murdered him, and he came back to life due to some quantum time Superboy, and decided to kill the Bat and all his allies.