Eliezer: Slightly edited the original post to avoid giving away what my readers have finally convinced me is, in fact, an undesirable spoiler. I also hope you didn't mind my removing the mention of FAI, because I feel fairly strongly about not mixing that into the fic. "A fanatic is someone who can't change their mind and won't change the subject"; if we can't shut up about FAI while talking about Harry Potter, we may have a problem.

(http://lesswrong.com/lw/2ab/harry_potter_and_the_methods_of_rationality/22cq)