I think you are assuming too much or not enough about the proceedings of various online communities in special cases. Sometimes, a thread will come a long on some forum, for instance, that starts out quite nicely. Then it develops into drama, HUGE drama - to the point of legal grey areas and further. So you gotta step in as a moderator and directly tell people to STFU & get a grip - but to allow "discussion" to continue from thereon is kinda pointless and perhaps even counter-productive. Personally, I wouldn't really want to check a dozen permasaged threads each day, and it's good to be able to point out to a thread that still exists as a form of responding to some frequent upcoming questions, even if it's closed.