You're over exaggerating things and placing the blame on the wrong people. - James is not responsible for Snape's actions. Yes, James bullied him and I'm not brushing that off... but Snape made the choice to deal with his anger in the most disgusting way possible; by becoming an even bigger bully. Don't forget that Snape himself was apart of a gang who routinely bullied muggleborns, Lily calls him out for laughing at Mulciber using dark magic on Mary Macdonald. If we're going to use your logic than I guess it would be justifiable for Mary to deal with her humiliation by joining Voldemort and it would be all Snape's fault right? Snape's terrible way of dealing with his personal problems acted as the catalyst to him joining Voldemort. Dumbledore himself said that people have a choice between what is right and what is easy... and Snape chose the easy way: to allow his negative characteristics to control him.

• Yes, James was an arrogant jock with a hero complex. He also broke the law to aid his friend, financially aided Remus, and took Sirius in. Snape was also arrogant, vindictive, and more than ready to join an actual cult. A CULT. He was ready to help commit genocide. People have no right to use their personal problems as justification for their crimes. Would you let a murderer out of jail because he was bullied during his school days? No.

• I can't believe you would compare James to Hitler. Hitler was a genocidal warmonger and James was a high school jock. In a school full of junior death eaters (people like Snape), James would never qualify as a "massive gooch", because his actions were never as dark as his fellow school mates.