I don't think heroes actually realize how special or rare they are.
Heroes think nothing of dying for a cause or for other people, and they never consider that they could do anything else. They see what they think is the right thing to do, and they do it, regardless of the cost to themselves. They know that there's a world full of darkness out there, and they wield the power of light to battle it, because it never even occurs to them to do anything else. They refuse to stoop to the level of the villains, no matter how tempting it may be - and they always seem surprised when other people do, because it never occurs to them that anyone with a shred of good in them could do that.
See, heroes think they're ordinary. They don't realize that most of us don't have a shining beacon of light and strength inside us. They're easy to disappoint, that way, because they can't imagine how anyone could ever be weak, or stupid, or wrong, or how they could try to do the right thing and do the wrong thing instead, or how they could take get in over their heads.
's hard to be around heroes sometimes. It's not like you can look at them and say "yeah, well, there was that time when YOU..." Because they've never fucked up, not like the rest of us have. They can't even fathom the impulses that make us ordinary types make terrible mistakes, because in them, those impulses are always overridden by something else. So they can't see why you would do something wrong unless you were just evil all along - because how could you not see? How could you not know? How could you think that you could just do that and the consequences would be anything other than terrible?
Darkness and fuck-ups and mistakes and selfishness aren't the anomaly. Heroism is. That's why people write books and movies and shows about it. Heroes just don't realize it - because they don't know that they're heroes. They think they're just regular people in extraordinary circumstances who did what anybody would do.
It's not just what anybody would do. What most of us would do is run. We would give in. We would sneak around to save ourselves. We would look darkness in the eyes and then we would scream like little girls and run crying into a corner, and we would do literally anything to make it go away.
I was a hero's kid. I tried to be one myself, but I wasn't very good at it. I was trying to do the right thing, but I think I probably chose wrong about as often as I chose right.
I guess what I'm saying is that it's not always as simple as these people being good and those people being bad. Sometimes it's just a person who's not built to be a hero getting thrown into a hero's spot in the story, or someone who could be a hero doing what they think is right and being wrong about it - so they get to be villains instead.