Doing the Job
You may think this is obvious. World domination is the good ol' standard villain trope, right? Of course I want to take over the world. I'm evil! And how do you know I'm evil? Because I want to take over the world.
Nobody ever seems to stop and consider that there might be good reasons for an evil dictator to be in charge of everything. Nobody ever thinks about how much better off a world ruled by an evil but (mostly) fair dictator with absolute power world be.
Why me? Well, because I don't think anybody else can do it.
Really, when you think about it, I'm just another starry eyed idealist looking to make change in the world. The difference between me and the college kid with the petition to legalize pot is that I stand a chance of actually doing something.