1- A classist excuse that ignores the social and economic conditions of a person in a situation of vulnerability and danger of social exclusion. The typical discourse comparable to that used by the neoliberal right to say that “whoever is poor is because they want to be.” You blatantly disregard all the material conditions surrounding a person from an extremely poor environment with no family support, only to find themselves in a school environment where they are constantly persecuted and harassed. You also overlook what it means to be embraced by a specific group of people promising to help them out of the misery if they follow them. Basically, you disregard all the international analyses and statistics linking young people at risk of exclusion as prime targets for sectarian and far-right political groups precisely because of their social conditions. But well, one can overcome classism too, especially when one reads books and not just fanfics and Tumblr posts.
2- He called Petunia a Muggle in a derogatory way after Petunia insulted him first for being poor. Lily basically ignored him when he shared his concerns about his group of bullies and even justified them. And no, an 11-year-old child raised in a Muggle neighborhood is not a DE from the start; he is simply someone who sees joining a particular house as an opportunity to leave his past behind. Villainizing that is, once again, internalized classism, but okay.
3- In fact, it is canon that he did not kill anyone. When Dumbledore talks about saving Draco’s soul, Severus retorts by asking if his soul is worth nothing. That is narratively designed to let the reader know that Severus did not commit such crimes during the war, otherwise his soul would already be condemned. Read the damn books and stop with the fanfics.
Moreover, yes, he is pardoned. And he is pardoned because any criminal who belongs to an organization but then actively collaborates with law enforcement to dismantle that organization, and provides crucial information to stop their plans, is usually pardoned for collaboration. You would know this if you didn’t live in the fantasy world of cheap fanfiction.
4- No, the reason was Voldemort as the murderer and Wormtail as an accomplice for betrayal. Severus warned Dumbledore months before the tragedy that the Potters were foolish to believe Sirius when he suspected Remus was the traitor, but that was their decision. Anyway, this does not negate the fact that, indeed, without Snape, it would have been literally impossible to defeat Voldemort, nor that he was the most relevant and competent agent of the Order, nor that thanks to him, Harry survived year after year. This is part of the books, and if it bothers you, tough luck.
5 and 6- What the colleague was trying to tell you is that double agents need to maintain a cover, and his cover was making it clear that he was still loyal to Voldemort despite working under Dumbledore’s leadership. In fact, in GoF, Voldemort himself considers Severus a traitor, so obviously, if he had known that, besides avoiding Azkaban, Severus was being friendly with Gryffindor kids, he would have hit him with an Avada the moment he saw him. Part of Severus’s survival method and having a convincing cover was indeed acting like a jerk to anyone who wasn’t a DE puppy. But given that you can’t follow a simple narrative, it’s not surprising you didn’t understand it. In fact, I have the feeling you probably still won’t understand it. Maybe you need drawings or perhaps to see this in one of those fanfics with OCs named after canon characters on AO3, because apparently, that’s the only way some of you can process messages.
And now, if all you’re going to do is keep throwing dirt on the most complex character of his generation, someone who came from a poor background and was marginalized for his appearance and poverty by a bunch of rich, white, aristocratic kids, I would recommend you save your social justice warrior posts for your friends because honestly, it’s embarrassing that some of you pretend to be progressive lovers of minorities when your fanaticism is based on whitewashing rich bully kids and justifying their abuse and mistreatment of a classmate in a socially and economically inferior position.
And yes, Severus was ugly, but I find it quite funny that you say this while claiming to be part of a fandom that advocates for inclusion. Are we adding body shaming to the classism and victim blaming? It seems so. Honestly, what a lousy education you must have had; maybe you have more in common with those DEs than Snape himself.