Voldemort doesn't want the world destroyed, and he just made Harry into a world-destruction-preventer. Pointing this out — and pointing out that Harry is now a better world-destruction-preventer than Voldemort could become — doesn't involve changing Voldemort's utility function.
(Voldemort can't swear an Unbreakable Vow akin to Harry's because nobody has trust in him that could be sacrificed to power it.)
He didn't make Harry into a world-destruction-preventer. He only made Harry swear not to actively destroy the world. Also, while Merlin might think that with all the effort Voldemort went through to prevent Harry from destroying the world it would be easier to destroy the world with a piece of cheese, I wouldn't find that so comforting.
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 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
There is 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.)