I just became aware of the original thread a few minutes ago, and much of the content was about the operation of the site, and had details that I didn't really like being made public. One of the guys that helps me with the sites violated the privacy and anonymity of a site user in the thread, and I thought it best to take it offline. As a user I would find it more offensive for messages to be removed from a thread than the entire thread removed.
Privacy of our users is of great concern to me, I've since removed the ability for admins to view reviews by site username other than when approving a review.
The only other reasons I have ever removed threads are when they contain "adult" words or SPAM. Not that I have problems with adult words, but having them in the content of the website can cause the site to get blocked by "family safe" internet filters.