Cannon!Snape has loved Lily since the two of them were children - considerably longer than 11 years. I don't think it's unrealistic at all.
I don't think it's particularly unrealistic coming from some unspecified hypothetical character who's just heard the love they've been harboring for more than half their life insulted, but I would find it pretty weird if Snape said that to Harry in that situation, and he wasn't exaggerating. Anyone who'd commit murder in that situation would either have to be profoundly lacking in restraint, or possessed by a really maniacal level of infatuation.
I suspect Snape was engaging in hyperbole, because if he wasn't my judgment of his character is completely out of whack.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 87. The previous thread has passed 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: