The Imperius curse is one of the Unforgivables. Using it to coerce a binder for the Unbreakable Vow is Not Allowed. The fact that being convicted of using it carries an Azkaban sentence probably prevents people from using it casually.
At best, the Imperius curse could make the Unbreakable Vow common in irregular society, the segment that casually breaks laws that could get them put away for life if they're caught.
I was more thinking of the Lucius Malfoy type. It is well enough established that the way the Wizarding legal system works, with a little bit of effort he can get away with almost anything. In addition, he seems to be the type of person to most benefit from Unbreakable Vows: That is to say he deals with many contacts, and most of them are not the most trustworthy people in the world (and that is putting it mildly).
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 87. The previous thread has passed 500 comments.
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: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17.
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: