Rescue Hermione. Use advanced magic and an FAI to heal the damage done to Hermione.
The "scary" or "horrible" thought is if he can't do this part. (Which to me looks plausible: if a 12 year-old girl gets sent to Azkaban then she almost certainly can't recover.) The taboo tradeoff would then look like this:
Option A : Rescue Hermione, but with some big utility downside.
Option B: Don't rescue Hermione, ever, but with some big utility upside.
Incidentally, one thing that no-one - I think - has mentioned is whether Muggle law carries any weight at all in this, since what Malfoy and the Wizengamot are voting for is a grotesque form of child abuse (and a huge taboo violation in Muggle society). Can they just ignore the civil law like that and get away with it : what if it led to a breakdown in the edict of secrecy (with Harry helping)? Are Hermione's parents going to be memory-charmed or fobbed off with some random story to shut them up?
Wouldn't this also be a form of taboo tradeoff - Lucius et al following through on Wizard law to avenge a blood debt vs keeping Magical Society secret? Or (from Harry's side) - breaking the edict of secrecy to get Hermione released vs Keeping it for the greater good (e.g. prevention of war).
Harry's Muggle parents could not authorize it because they were Muggles, and Muggles had around the same legal standing as children or kittens: they were cute, so if you tortured them in public you could get arrested, but they weren't people. Some reluctant provision had been made for recognizing the parents of Muggleborns as human in a limited sense, but Harry's adoptive parents did not fall into that legal category.
I kinda doubt wizards in general care overmuch about Muggle law.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
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: one, two, three, four, five, six, seven, eight, nine, ten.
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: