Harry only promised that if he found out who did it he would take them as his enemy. Bad things don't happen to Harry's enemies, weird things happen to Harry's enemies. I don't think Harry will have any moral qualms about making weird things happen to Dumbledore.
We've never actually seen Harry deal with a real, deadly enemy before. When he pledges to take someone as his enemy, in the formal way he did when Malfoy told him about Narcissa, I think what he's talking about goes beyond the level of schoolyard bullies and annoying reporters.
(The HPMOR discussion thread after this one is here.)
The previous thread is over the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it. The latest chapter as of 09/09/2011 is Ch. 77.
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. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, 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: