What can I say? Villains have more fun.
To be fair, the best kind of villain is an angsty villain. You know the type. Probably had a rotten childhood, didn't get as many nuclear explosives as they wanted for Christmas...
No doubt this trauma explains why they are trying to destroy the world/kill the hero/kidnap and or rape Miaka...Then again who hasn't?
Mind you, I am not here to defend them. I won't say "But he was warped by tragic backstories!" I'm more likely to say, "And he's so HOT!"
The evil being just an added bonus.
Disclaimer: You do not need to be a meglomaniac, pyro, psychotic, sociopathic, or just generally evil to enter this site. Really. But it helps.