Everythings a choice. Nobody's born good. Nobody's born evil. It's always a choice.
We're all flawed heroes. Responsibility is power. Take responsibility for the consequences of your actions, and the world is yours. Everything is a choice.
The difference between a hero and a villain is that they just make different choices.
I suppose my understanding of villains is that they're just people who are infected by all of the darker instincts - that they haven't got the discipline to make the right choices.