For whatever reason, I’ve been thinking about Severus Snape a fair bit lately. Per Rowling, he is portrayed as an essentially good guy who made some bad decisions early on, had a prickly personality, but was ultimately courageous and redeemed by love. Being portrayed by Alan Rickman certainly didn’t hurt either.
After a lot of thought, I don’t really buy that assessment. Was Snape courageous? Perhaps at a couple points, in planting Gryffindor’s sword and his final scene with Voldemort. Do those moments redeem him? Do they make him heroic, good, or even sympathetic? I don’t think so.
First and foremost, Severus Snape should never, ever, have been teaching. From what we see of his actions and his statements throughout six books, he clearly hates teaching. He may even hate children. And he tends to target the weakest subjects (Neville, Hermione the Muggle-born, at first). His attitudes and behavior are right out of a Pink Floyd song (you know the one).
Compounding this is his blatant use of favoritism, which we do not see among the other teachers. In fact, Ron specifically states that he wishes McGonagall would cut them a little favoritism. And we can’t say that Snape does it because of being Slytherin. Slughorn, so far as we see, never plays house favorites—despite his talent or connections based favoritism and his casual “You mustn’t think me prejudiced” racism. This behavior is a continuation of his childhood vendetta against a particular group based of stereotyping.
In his silence regarding Malfoy and others in Chamber and onward, it is also possible that Snape retains a portion of his childhood racism. That he had the seed, we see in his treatment of and language with Petunia during their childhood. It fully germinates at school when he joins the Death Eaters (his memories).
But, we know Dumbledore uses teaching posts to protect assets, regardless of their actual teaching ability (ref. Trelawney).
Second, I think Snape’s connection to Lily was not love. I’m sure I’ll catch some flack for that. But, I think he became fixated on the first, and only, person who ever showed him kindness without ulterior motives. While we know little about his childhood, what we do see implies that he was probably poor and, unlike the Weasleys, likely abused, possibly even witness to domestic violence. Then he met Lily at the age of 10, give or take a bit. And she was fascinated by what he was able to do, and she looked past his oddities and economic status, and treated him well.
Dumbledore was, of course, somewhat kind too. But, Dumbledore had other motives—his desire for a double agent and his recognition of Snape as an early warning system (since he was certain Voldemort was not gone) that led him to keeping Snape close.
The Malfoys are also relatively kind to Snape. But, they see him as a useful tool, or a servant, someone to whom they go when they need something. The class issue is always there between them.
Lily is the only one who interacts with Snape in a positive way without ulterior motives. In return, he continually tries the “Nice Guy” routine (or Syndrome) with her. Even when she brings up the Death Eaters-to-be whom he hangs out with, he falls back on “You’re different. I’ll protect you from them.” He seems to assume that because she’s nice to him, she is attracted to him. And that simply being nice to her cancels out anything else he’s done and should make her attracted to him. It’s not love. It’s a form of possessiveness. He wants the one person who has been kind to him to be his and never leave. It’s really not a healthy relationship, on his end. (On Lily’s end, she eventually sees that Snape’s treatment of Petunia, and the attitudes that underlie his actions, is not something he’ll grow out of. So, she moves on.)
Ultimately, Snape is, developmentally, stuck in childhood, despite his claims to logic and reason. He is stuck in a fixation on the only person who showed him kindness (his patronus is a doe, which Rowling implies indicates his love for Lily, but, I’d argue, indicates his happy memories of someone being kind to him). As part of this, he is mired in a childhood feud (like Sirius, who also remains stuck in his childhood glory days, for different reasons) turned vendetta due to a sense of entitled possessiveness.