The problem is that as Dumbledore is written in the books, he's either a cartoonishly evil old man, a senile old man, or a psychopathic old man that's trying to be good.
I like to believe it's the latter. Psychopathy isn't actually all that rare, most people just learn to consciously emulate a conscious/empathy to make up for the lack of one. When you take into account that Dumbledore is probably forcing himself on the muggleborn issue, and what happened to his little sister, you can imagine that it's not a great combo.