I think it was implied that the memory wasn't the cause for Harry being able to see Thestrals; Harry seeing Death in the form of a Dementor was. From Chapter 49:
"They are visible only to those who have seen death and comprehended it, a useful defense against most animal predators. Hm. I suppose that the first time you went in front of the Dementor, your worst memory proved to be the night of your encounter with He-Who-Must-Not-Be-Named?"
Harry nodded grimly. It was the right guess, even if for the wrong reasons. Those who have seen Death...
If comprehending the nature of Dementors is required to see Thestrals, how does Quirrel - or anyone else - see them? Quirrel seems to accept that "seeing Death" means simply seeing someone killed, perhaps someone dear to you.
Edit: New thread posted here.
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 86. The previous thread has long 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.
As a reminder, it’s often useful to start your comment by indicating which chapter you are commenting on.
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: