You and I are, by birth, by nature, and by choice, inwardly depraved, which is to say that we are entirely corrupt. That's not to say that we have no good in us; we do. However, anything good in us has been tainted with evil. It touches everything. Without the redeeming power of Christ we cannot halt our own moral slide.
A properly balanced story provides an equal representation of the negative and positive attributes of, I could say the world, but it's actually a being. 'Harry Potter''s a good example. So Harry's the hero, right. But he's tainted with evil. There's a dark and a light in every bit of that narrative. It's well balanced.