Every drama needs a conflict. Tales of conflict are easier to tell with pure heroes fighting pure villains. Simple enough for children to understand. The Red Skull was a bit better as a villain. One of the best villains was Doctor Doom. Why? Because he was not purely evil. He was a complex character motivated by deep loyalty to his nation. At least, that's the Doctor Doom I remember. They've probably ruined him by now. Anyway, we're still talking about silly cartoon characters right?