So, as the title suggests, the ideas within this post were crystallised while watching X-Men First Class. Don't judge me, okay?
What struck me while watching - watching all the X-Men films in fact - was that while Eric/Magneto is unquestionably the bad guy...I couldn't help rooting for him, just that little bit. That I actually sympathised with his position, even while I disagreed with how he went about things. Because he believes utterly in his position, as much or more so than Charles even. From his point of view,from his experience, mutants will be experimented on and used as weapons. Charles likes to think that humans are essentially better than that, but Eric knows that they aren't. And what's more, he isn't wrong either.
Another example of a character I think made a fantastic bad guy is the Assassin from Serenity. He knows, without a shadow of doubt, that what he's doing is wrong, evil even. He also knows without a shadow of doubt that he's making the 'verse a better place, even if that better place has no room in it for him. He believes utterly that he is doing the right thing.
It's often been said that a villain, or any character, is the hero of their own story. And how much better does that make the conflict? Two people, with opposing wants/beliefs, who both believe they are the good guy. That they are right and good. The road to hell is paved with good intentions, and that's reflected in all the best bad guys. Magneto wants to save his fellow mutants from being controlled and experimented on. The Assassin wants the people of the 'verse to have a better place to live. Grendel's mother just wanted revenge for Beowulf killing her boy, a very human emotion. In Bladerunner, Roy Batty wanted the chance to live longer, to keep those memories of C-beams glittering by the Tanhauser Gate alive.
While I can appreciate a bad guy being bad cos he just is, okay? I'd much rather have a bad guy with real, relatable reasons for doing what he's doing, a bad guy who believes in what he's doing as much as the good guy. It makes the conflict just that bit more piquant, that little bit more ambiguous, that tad more engaging and thought provoking. It gives the whole story some depth that a moustache twirler so often just lacks.
I love that in a story.