A war means people risk death, Voldemort or not. The last plot tried to have Hermione die in Azkaban, and (since Harry doesn't believe Quirrel did it) seemed designed to kill Draco right away; the next plot may succeed. And people are dying in Azkaban all the time, second by second.
Pre-edit Harry was unwilling to commit to killing as an acceptable instrumental goal given a sufficiently high payoff. Making a goal sacred and of infinite value, while also wanting to balance it with other terminal values, is a contradiction. Harry realized this, and did it anyway, and that is a rationalist sin. He disobeyed the rule that "if you know what you're going to think or do later, you should think or do it now".
Post-edit Harry is willing to commit to killing if that's what it takes. He asks Moody not to harm the suspect if possible, but he doesn't say they should not attack him if they expect to have to harm him. He is both a better rationalist and a better person.
The thing is that people aren't perfect rationalists, and part of being a good rationalist is acknowledging your own flaws and limitations.
If you accept to kill, you'll kill, even in situations where killing wasn't necessary, because you'll stop searching the hypothesis space when you find a solution that involves killing. Or because you'll estimate that killing one will save two, but your estimation was flawed - you killed one, and yet the two still die. And it's also something you should know about the way humans work, that once you did something once, i...
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: