This applies to both protagonists and antagonists. I know it's a bit of an obvious stamp, but I posted it anyways regardless.
I swear, out of all Mary Sue qualities that could be given to a character, the "pure hearted, innocent" type is the worst of all. I'm talking about those so called "heroes/heroines" who NEVER EVER commit acts of sin (intentionally), are willing to sacrifice their lives for people they don't even know or people they hate, doesn't show a single hint of selfishness whatsoever, and behaves like morally flawless angels no matter what the circumstances are. And if they DO commit a sinful act, it's always justified from a stand point.
Then there are the villains- the typical "badass" whose ambitions are to be the BADDEST OF THE BADDEST AND THE MOST EVIL BIENG IN EXISTENCE. They have have no mercy, no passion (except for being evil), and absolutely no remorse for whatever they do.
Black and white characters IMO are boring and don't allow any room for development. An well balanced character stays trapped on neither ends of morality. Some may lean towards one side more than the other, but not completely. Especially if your character is human. Even the most nicest of people have qualities that are wrong and sinful, and vice versa when it comes to villains.
Yes, I've seen these in original stories as well as fan fics. (but mostly fanfics)