Great point!
However, in TSPE arc, when Harry had one of his emotional "I'll destroy all dementors right now" episodes after hearing just how Bella was used by Voldemort, he had to come up fast with rational reasons not to do it. And one reason was that it would not be maximally efficient to destroy the dementors while standing in a corridor in Azkaban, and it would be better to go himself to the central pit where they lived.
So it should be much harder yet to destroy them from Hogwarts. Maybe not impossible, though. One at a time?
But Dumbledore would immediately know that it was Harry doing it, and would stop him after only a few were destroyed, unless he managed to destroy them all in one go. And Harry's internal monologue in the same instance I referred to indicates that doing so would take so much life-energy it would kill Harry.
And one reason was that it would not be maximally efficient to destroy the dementors while standing in a corridor in Azkaban, and it would be better to go himself to the central pit where they lived.
I guess the question is whether it's Harry's location that matters or the location of his patronus.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
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: one, two, three, four, five, six, seven, eight, nine, ten.
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: