I understand you being tired of such ideas that do not stop despite the evidence. However, by what justification can we ban them, and not many other frustrating topics? Surely you must be equally over anti-vax by now. And what about homeopathy? Homeopathy is always my favourite pseudo-science to use as a baseline, because it is so easy to provide evidence that it has absolutely zero merit, and yet there are institutions (still!) dedicated to teaching it.
If we let personal frustration be our guide, many topics will be banned - topics that people believe in, topics that misinformation abounds in, and topics that people will search for in Google for reliable information.
If we accept the premise that there is a marketplace of ideas, and the best ideas with the best evidence will win out, we need to keep plugging away. (I admit I have difficulties with this idea when it comes to ideas that are not held rationally; sometimes I feel the best response to a conspiracy theory is not a debunking, but a referral for psychological evaluation, but alas that choice does not appear in the list of tools available - even to moderators.)
Until that becomes available, the best we can do is make sure that the questions are dealt with rationally and with evidence. Even if we can't persuade the irrational, we might be able to persuade the borderline cases that have heard the ideas and want to check before committing to them.
Actually, the best we can do is to provide a single canonical answer that thoroughly and completely demolishes all of the common crank theories, so we can simply reference it from all the other questions as they come up.
p.s. The irony that we would conspire here to suppress questions about 9/11, because there are no conspiracies to suppress questions about 9/11 is not being missed!