Not unexpectedly, I disagree with Byrne. A lot of comic book villains need some motivation and reason for being what they are. In a genre that lends itself to absurdity, such grounding keeps the characters from being a joke.

In the case of Two-Face, if you take away the Harvey Dent aspect like in the scans above, you present a guy who has all the stupid parts of being a supervillain. Stupid name, stupid gimmick, stupid plans. You're back to the old days of wondering why Harvey doesn't just shoot Batman when he has a chance instead of going through his long monologues and poorly planned death traps.

Aside from all the storytelling potential that a partly sympathetic villain has, having a guy be evil through and through reduces supervillains to the status of bad Bond villains. They need a reason to do what they do, or they're reduced to jokes in most people's eyes.