Some men aren't looking for anything logical. They can't be bought, bullied, reasoned, or negotiated with. Some men just want to watch the world burn ~ Michael Caine; The Dark Knight
I don't think that quote does suggest that he's evil just for the hell of it. It suggests that he doesn't expect to gain anything from his evil acts, but there's still a reason why he does them. We don't know what it is, but it's there. I would assume he's suffered some sort of trauma in his life - see those scars? They came from somewhere, right?The person with the quote about the Joker is interesting. The quote sounds like he's just evil for the hell of it, but truth is he was one of the most complex villains I've ever seen. Actually, they did an awesome job with Harvey Dent, too. I wanna go watch Dark Knight again now haha.
Damn, now I want to watch TDK again...