I guess I always see taking over the world in four voices:
1) Superiosity: "Dude, you are so much smarter than everyone else. You could solve all the world's problems in 2 minutes flat if you had absolute control."
2) Practicallity: "You'd suck, because people are stupid, and you are a people."
3) Paranoid: "Oh, yeah, sure, that's a great idea: get them all mad at YOU."
4) Lazy: "Ugh, work. Just sit back and watch them debate about nothing. It's free."
For these reasons when a villain gives their whole monologue about what grand reason they have for wanting to lord it over everyone it actually makes less sense to me the more real their character is. I think this even extends to regular bad-guys like gangsters and such. When you have a cartoony villain who is obviously made to silly and they give some totally wacky reason they're doing everything it just somehow becomes real because it's giving in to my vision of the stupidity of being a villain.
I guess I'm just weird that way. :D