I like to discuss the characters and their motivations.
As do I, which is why it's nice to know we can just have fun with this.
And he knows without a doubt that he can trust her.
Perhaps this is one of those points where our character interpretations differ dramatically. I think he is too damaged to trust her at this point. Particularly when she says things like, "And now I’d better go before you learn about even more of my sins."
I do think he would trust her to the extent that he would expect that she would not betray him so long as it fit in with her goals. She has repeatedly shown the type of ruthlessness that makes her a great ally, so long as she believes that she needs you. But her flaws (what I term her character defects) are such that I just don't think he would trust her to stand by him through thick and thin. And her crack, "Should I now start adding up everything that’s been done by Slytherins?" pretty much proves that.
BTW, YES, I know he's not much better, with his slam on Gryffindor hypocrisy. Also, at least he limited his slam to "just" her overwhelming hypocrisy, self-righteousness and lack of forethought. ;-) But I do think you nailed him there, in that he really would react that way and let spew out a little of all that bitterness that's been festering for decades.
And don't forget: canon Snape loved Lily. The type of woman he finds attractive doesn't have to be perfect. Neither is he.
Absolutely with you there. Sometimes, I forget that I need to state outright that Snape can be a petty, vindictive, nasty person, who (as you may recall from Snapedom) I have pointed out was a Death Eater---not exactly known for charm and charisma. It's just that he has all those wonderful qualities bundled up with it, drat it all. ;-)
On the Edgecombe issue, though, we probably will have to agree to disagree. Which is unfortunate, because to me it is the epitome of what is wrong with Granger. To put on a hex that would disfigure somebody only AFTER they have betrayed people, to not come up with something that would, for example, stop them from speaking about the DA except to certain people, let her know that somebody WAS talking about the DA, and above all, NOT to say anything, meant that the DA had no protection. There was absolutely nothing stopping Edgecombe from telling her mother about the DA, nor did it give any warning to the DA that they were about to be raided. So, in my book, it was completely ineffective to protect the DA. Sure, it would have inhibited others from talking...but only AFTER the damage had been done. And she is proud of it and how clever she was. And it was a clever hex, but totally ineffective to her purpose.
She was even younger then, and faced with dangers no child should be faced with.
Yep. Although, to be fair, those children chose to take on a great many dangers they did not have to. Just look at the mess with Quirrell. If they had sat back, if Granger had not "solved" the logic puzzle, if Harry had not gone into the room with the mirror, Quirrell would have had no chance of getting the stone. They inserted themselves into danger needlessly and almost helped Voldy win, out of nothing more than officiousness. ;-)
You may note that Sev didn't chastise her for using questionable spells, but for not taking the consequences for herself into account. And for pretending to be morally superior.
Well, there's not much point in chastising for questionable spells, is there? That's not what he's trying to teach her. He's trying to teach tactics and strategy. And what bugs me is her refusal to *think* about those things. To me, it just shows that she's not really all that bright. She can regurgitate stuff she reads, but she does not put in the effort to analyze and think it through. And by this point, she's old enough to know better.