I think his "humanization" taught him the difference between what is right and wrong. I think that Lily's death gave him a sense of empathy, and perhaps a better understanding of his actions and their consequences.
See, I don't because there's the whole of Snape's treatment, not just of Harry, but of Hermione and some of the other students throughout the series. I'm a firm believer in the idea that how you treat people from *day to day* -- not just in emergency or crisis -- is a reflection of your character, both moral and ethical. Prior to DH, I might have bought that Snape's conduct was a function of his cover as James Bond a double-agent, but the memories in DH demonstrate that he really was an extremely unpleasant person. And even that could be okay -- you (general 'you') can have a cranky demeanor but still make truly decent, ethical choices. But with Snape, I keep going back to that conversation he has with Dumbledore in the memories about how he actually didn't care if James and Harry (an infant!) died as long as *Lily* didn't. It leaves me thinking that his love for Lily didn't really change him so much as made him susceptible to Dumbledore because of the way Snape thought he'd betrayed that love. Even later in the memories, when Dumbledore suggests that Snape has come to care for Harry qua Harry, Snape reacts indignantly to that, producing the doe Patronus to remind Dumbledore that it's still really All About Lily.
None of this is to say I think it's *bad* that Snape does all he does out of love for Lily/Lily's memory. It's just that I don't think it makes Snape *good* in the way I think a lot of people were hoping it would be revealed that he was good. This is why I used the Narcissa parallel: she thwarts Voldemort by lying to him that Harry's dead and she tells that lie out of love for her son, but I don't think anyone would seriously claim that it suddenly means Narcissa is good or noble or honorable; it just means she loves her child enough to risk Voldemort's wrath to keep him safe. Snape loved Lily enough that he's willing to risk detection to make up for the fact that he contributed in no small part to getting her killed.
part I
See, I don't because there's the whole of Snape's treatment, not just of Harry, but of Hermione and some of the other students throughout the series. I'm a firm believer in the idea that how you treat people from *day to day* -- not just in emergency or crisis -- is a reflection of your character, both moral and ethical. Prior to DH, I might have bought that Snape's conduct was a function of his cover as
James Bonda double-agent, but the memories in DH demonstrate that he really was an extremely unpleasant person. And even that could be okay -- you (general 'you') can have a cranky demeanor but still make truly decent, ethical choices. But with Snape, I keep going back to that conversation he has with Dumbledore in the memories about how he actually didn't care if James and Harry (an infant!) died as long as *Lily* didn't. It leaves me thinking that his love for Lily didn't really change him so much as made him susceptible to Dumbledore because of the way Snape thought he'd betrayed that love. Even later in the memories, when Dumbledore suggests that Snape has come to care for Harry qua Harry, Snape reacts indignantly to that, producing the doe Patronus to remind Dumbledore that it's still really All About Lily.None of this is to say I think it's *bad* that Snape does all he does out of love for Lily/Lily's memory. It's just that I don't think it makes Snape *good* in the way I think a lot of people were hoping it would be revealed that he was good. This is why I used the Narcissa parallel: she thwarts Voldemort by lying to him that Harry's dead and she tells that lie out of love for her son, but I don't think anyone would seriously claim that it suddenly means Narcissa is good or noble or honorable; it just means she loves her child enough to risk Voldemort's wrath to keep him safe. Snape loved Lily enough that he's willing to risk detection to make up for the fact that he contributed in no small part to getting her killed.