I think that was probably the main reason. He just couldn't take any more of what he knew was wrong. If he had lived with it much longer, I think he would either gone mad or turned racist himself. The Potters would have been inspirational to him, and a much happier family.

I just realised, he wouldn't have fitted in with the family, and he might have been threatened by his father or someone to join the deatheaters or die. Sorry, I'm rambling on again, aren't I...