Also not those who have appeared very marginally and have not been actually characterized (Flitwick, Trelawney). We also have no reason to attribute motive to one of them.
How's their motive relevant if they're under imperious?
You're right, the Hogwarts wards don't detect or prevent Imperius cast by and on professors. That actually makes sense to add extra deniability for Quirrel (or whoever is controlling them). Edit: either I didn't see this part of the grandparent or I didn't realize the implications.
However, either the Imperius must be maintained indefinitely: too much risk of being found out one day? If something happens to the controlling character, short of death, does it provoke a Will save and break the Imperius? If the controlled character is examined, especially by a ...
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: