Harry's dad led Snape to join Voldemort

I think it was important for Harry to realize that his father was not perfect. That he was human, including being an arrogant punk as a teenager. The world isn't always black and white, and it can be hard to tell the good guys from the bad guys. I feel Harry really has to learn this before he can wage war against Voldemort and decide who to trust and who to ally with. He needed to understand that even the deatheaters were human, and had feelings and motivations like everyone else. It was obvious that Dumbledore, while loathing the things Tom Riddle did, had compassion for the young boy that was shaped largely by circumstances into the adult he became. I think that Harry needs to learn to have that same compassion, and perhaps learn from his father's example and not let his considerable talents make him arrogant or unkind.

I don't think so. Nobody should be held accountable for our actions but ourselves, so we can't blame James for how Snape turned out. If a person is inherently good then no matter the provocation he will stay good. In Snape's case I think that even without Jame's bullying he would have ventured eventually into the dark path because he has long been fascinated and obsessed by the dark arts. I think that like Voldemort, Snape was seduced to the dark side by his desire for power not because he was bullied by James Potter.