Snapedom

Although I do sort of understand what you are saying about Dumbledore and some of his decisions were definitely Machiavellian this is not the same as being bad. Also Snape is a really dislikable person he is a bully just accept that statement, he bully's children under his care which is fundamentally different from bullying a peer, because of the position of responsibility, he was foul to Harry even when he first met him. This is childish, spiteful and the marks of a very poor teacher. With Lily he thought that dark magic used against an innocent girl was funny, he called his best friend a "Mudblood" publicly they had been friends for five years, she did not immediately brush him off as soon as they got to Hogwarts not being friends anymore with someone who calls you a racist slur, uses dark magic which can be clearly defined as different to hexes and wants to become a member of a group seeking to eliminate you and people like you is a perfectly reasonable course of action. In the shrieking shack scene what is on the line is Sirus and maybe Lupin to having their souls sucked out this is a major over-reaction to a what Remus is correct in stating is a "school boy grudge". We only see a couple of scenes of the interaction between James and Snape all from Snape's point of view. Snape is highly capable and perfectly able to defend himself, that curse that curse he used on James and in the Half-blood prince secptumsensa which I can't spell was labeled "for enemies".