Threads can be deleted but we don't like to do it often and will not usually delete a thread apart from in exceptional circumstances. These include:
Libellous threads. If we think a thread might be libellous it might be deleted. This hasn't happened very often.
Personal threads. If a thread is started discussing a registered user or their actions, that user has the right to ask for it to be deleted or locked. The thread does not have to be an attack on the user. This does not apply to threads users start themselves and later regret.
Offensive threads. At their discretion, moderators can delete entire threads which are likely to cause offence. It happens very rarely - threads which are racially or sexually abusive are the most likely. Even then moderators might not delete the thread, if an offensive question seems likely to provoke debate. If you find a thread offensive, please say on the thread or email a moderator about it.
Test case establishing precedent? Maybe. But either delete the thread (and any copycats that result) or change the moderation rules.
― Masonic Boom, Tuesday, 1 April 2008 15:33 (seventeen years ago)