I wrote this post in response to this thread, which got closed before I could post it. (Which is annoying, by the way – does it really hurt anything to give people a chance to comment on mod actions?)
So, leaving aside this particular case, I’d like to express my general dissatisfaction with the policy of deleting any active thread with more than a couple of replies, regardless of who started it. You’re not accomplishing anything, you’re just giving the sock way more attention by annoying the rules-abiding posters who suddenly can’t find the thread they were just posting in.
Want to discourage a sock? Just ban him, put a brief mod note in the thread saying “OP was a sock, carry on” and if you’re feeling particularly bold, leave the thread open so people can have fun at his expense. People having fun is a good thing, and far more important than maximizing the Internet Justice that is dispensed at the socks and trolls.