Keep in mind that while on the one hand, memory charms are a crazy broken superweapon for anyone with a bit of unrestrained creativity, they also seem to be a standard response for ordinary wizards on the spot dealing with muggles who've caught a slip in the Statute of Secrecy (for instance, a rampaging dragon.)
Counting against this observation is the statement that they're "illegal to use without Ministry authorization". Counting for it is the fact that Quirrell and the other villain candidates seem happy to use them whenever convenient with no negative consequences. Given that the Ministry apparently has a magical net capable of instantly detecting underage spell use, it's odd that they seem completely unable to monitor the use of conditionally legal, illegal, and Unforgiveable magic.
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 90. The previous thread has passed 750 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, 17,18,19.
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: