My (not so well-read) opinion is that the stark good/evil contrast in comic books, H/Bollywood movies, etc. comes from thoughtless readings of the embodiments of Good & Evil in our scriptures. To my non-fundamentalist eyes, these are devices to help us distinguish the good from the evil, which are inextricably linked within and around us. Furthermore, most religions that concern themselves with this dichotomy also advise against judging an individual Good or Evil, leaving that to some human-transcending entity, for instance. There's a good reason for that, I think: all that constitutes our existence is anything but absolutely discernible as one or the other of these moral poles. Yet, distinguish between these we must, often in absolute terms, in order to live up to our morality, however we may define it.
Aaron's "intentionality" remarks reminded me of the movie Seven, about a serial killer who kills those whom he considers indulging in one of the Biblical "seven deadly sins." He of couse believes not just that his intent is good, but that his actions are Good. So conscientious is he that when he finds himself guilty of one of those sins, jealousy (or is it lust?), he surrenders to the authorities, asking for the same punishment that he meted out to his victims. There is a moral consistency here that is rarely found among us normal folks, most of whom agonise over the minor and major moral inconsistencies of our thoughts and actions, never ever managing to eliminate them. I, for instance, buy sweet and juicy strawberries from California, quite aware that most of the migrant workers who picked them are paid sub-human wages and have no access to any of the basic benefits that Americans enjoy. Still, I want to see my aging mother enjoy the strawberries, and these are the only ones I can afford on my limited budget. Who's the evil one, the conscientious killer of Seven or I, the wishy-washy liberal?
So, re. "Everybody thinks they are good," I don't think that's true. Most people know they cut moral corners and rationalize to varying degrees. People's moral compasses are also not calibrated to comply to a single standard. People make conscious choices to act in morally deficient ways, sometimes even talk themselves into doing so, as they negotiate through their respective obstacles toward desirable outcomes for themselves and those they care about. What separates them from the comic book villians is not that they always intend to do good, but that they intend to do good but are not above the opposite intention either.