Villains, in my view, should be forged from the settings and backstories they come from. In some instances you could have them created knowing absolutely nothing but an insatiable lust for <x, war, food..> like the levvies from supernatural. Or, and what may end up as more interesting of a character, you have ones that came from a situation that changed them. Some event, influence by another, discovering something to change their philosophy. They could be driven to a single cause that people would think is evil but really comes down to your perspective (revenge, perhaps).

You could also have an anti-hero character, or someone who isn't necessarily evil, but takes causes that would be to the majority morally incorrect to reach a just end or at least something that they feel would make the world better. In the end, I think it all comes down to the motive.

I'm hoping that tackled the asked questions, just something to think about.