I wasn't that happy with that plan to begin with, but the more I've thought about it, the more I've started to like the elegant simplicity of it. He'd get tremendous political turmoil, and possibly throw suspicion on himself with respect to the Bellatrix breakout, but he can still deny that, and they've got another suspect anyway. At the same time, he has a chance to sink Azkaban in one shot. I'm calling this one the Damn The Torpedoes Option.
In his place though, I wouldn't necessarily encourage them to find out how I did it (he can resist veritaserum and leglimency,) but I'd tell them that it's already too late for them to stop the dissemination of the spell, thus rendering dementors and azkaban obsolete.
Bluffing would be dangerous - if he doesnt actually publish the information, killing him makes the problem go away. And if he commits to "Tell the world, make dementors useless" Then the wizengamot entire are simply more information pathways, and are in fact far better ones than just about anyone else he could tell because it is much harder to obliviate them than Jane Q Wizard,.
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: