"It takes a cracked soul to cast." and "Murder tears the soul." just says that if you've gotten to the point where you could cast it once, that particular pre-requisite is already accomplished, so the work to crack your soul is already put in. It doesn't say anything about removing the requirement of wanting someone dead.
Though, so long as we're looking at evidence, if we take Quirrell at his word, then his ability to cast the spell despite not wanting his opponent dead is pretty strong evidence that the requirement is in fact removed. In fact, we already know that some "requirements" to cast spells are not set in stone: from that same scene, Harry cast the true patronus without the carefully practiced stance and wand twitches, instead merely "one desperate wish that an innocent man should not die -"—but the constant requirement in this case seems to be the thought that accompanies the casting of the spell, which is why I'm hesitant to believe the wish of death is removed from AK's casting requirement.
Though, so long as we're looking at evidence, if we take Quirrell at his word, then his ability to cast the spell despite not wanting his opponent dead is pretty strong evidence that the requirement is in fact removed.
Just because he didn't intend to kill him doesn't mean he didn't want him dead. As Moody said, you have to want it, not just for the greater good, but as an end unto itself. Quirrell might have wanted to kill Bahry as an end unto itself, whereas for matters of convenience it was better to leave him alive.
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: