On the other hand, its not a new idea. Harry mentions that some wizards used to wear armour in the dark ages, and they probably wouldn't have stopped using it if it was useful.
In Eliezer's HPverse, that may be a sensible argument. (Given the general irrationality of wizard-dom, not a very strong one, though.) I'm criticizing Eliezer for diverging from canon, which IIRC has no suggestion that armor would be useful or had been tried but abandoned in the past. (The only example I can think of is maybe canon had goblin armor, and I'm not sure how that would apply.)
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
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. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, and AdeleneDawner has kept an archive of Author's Notes.
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: