10. He's Insane
It's an easy joke, but a good one.
"Batman? Oh, you mean that guy who had a psychotic break when he saw his parents shot in front of him, so he decided to dedicate his life to a totally unhealthy exercise regime in order to wage a one-man war on crime? And he does it whilst dressed as a six-foot tall giant rodent? That guy must be nuts, right?"
That's a common argument trotted out against the Dark Knight, and it should be noted that it's one that Batman villains use it all the time. "We're not so different, you and I", and so on.
There are some similarities between the hero and his rogues gallery - that's what makes their confrontations more interesting than him just, y'know, fighting evil dudes. But they key difference between them is what makes Batman the hero, and the rogues the bad guys: Batman isn't insane.
It's sort of patronising and problematic to assume that somebody who goes through massive childhood trauma is going to go nuts, and more than a little cynical to deem somebody who wants to change the world for the good as bad as the criminals they're fighting.