This chapter may sort out something which got on my nerves earlier in the story-- the long sequence where Quirrell is Harry's only friend. I'm not saying that Harry should have known Quirrell was Voldemort (and I still think it might have been more interesting if Quirrell had been seriously bad news, but not Voldemort), but it seems to me that Harry liked and trusted Quirrell more than he should have. (Sorry, no details-- I'm going by memory.)

I always found it extremely plausible. Harry has had an isolated childhood, by his own admission, lacking in friends, in intellectual equals, in people who would take him seriously. Quirrell is the first person he's met who thinks like him and is better at it and who gives out approval but in a sparse fashion. So we have a kindred spirit and a role model to admire (intellectually if not ethically) and a parental figure to dispense the sort of validation Harry can't get anywhere else. Quirrell pretty much ticks all the boxes for Harry, in a way no one else does. If Quirrell was actively trying to brainwash Harry, he could hardly have set up better conditions.

It's interesting that a kind upbringing can have such a large effect, but I'm not sure this makes sense-- why wouldn't more of Quirrell's misanthropy have carried over?

Quirrell doesn't hate people so much as he has given up trying to care about them after being bewildered and frustrated by their flaws. His Killing Curse is powered by indifference, not hate. Harry's scientific background makes it easier for him to understand why people are flawed in the ways they are, and it gives him hope that they can be improved, which is something Quirrell never had.