ok first of sorry if this makes no sense.

I agree that just because James and friends bullied him does not give him reason to become a death eater and kill people however, I do belive that the way he was treated in school resulted in the resent he felt towards Harry what with him being so similar to his dad in many ways (except the whole bully part). I also think that if it wasnt for Snapes love for Lily his attitdue towards Harry would of been alot worse, After all it was sort of his love for Lily that spured on his final act of helping Harry out in the Deathly Hallows.
Going back to the him being bullied in school, like i said it gave him NO excuse as to where he lead his life but there is the slight thought of perhaps if he was accepted more in school by James and the rest of the mauraders then maybe just maybe he wouldnt of taken the path he did, there is a chance that he chose to take the path of dark purly because he felt like he belonged and was accepted whereas if he was allowed to be proper friends with Lily as well as the mauraders then there could of been a chance that he would of been on the right side of the fight and perceived as one of the "good" guys all along.
You have to look at the big picture though: If he wasnt the person he is then where would the big story be in the end after all there has to be at least on bad good guy (or should that be a good bad guy) in every story to make it interesting

Ok im done now i think, again i appologise if none of that made sense but thats how i feel about the situation