The comments about crackpottery in Physics Forums Global Guidelines seem to deal mostly with the personal physical theories, and not conspiracy theories. But this thread https://www.physicsforums.com/showthread.php?t=177337 seems to indicate, that you do have some kind of policy conserning this. The WTC conspiracy isn't really scientific crackpottery, but political instead. By this I mean, that even though some specific claims made by the conspiracy theorists are not very convincing, the big idea that explosives were used to bring buildings down, does not contradict laws of physics, it contradicts certain political atmoshpere. Since the purpose of moderation is primarily to maintain certain scientifical quality in discussions (and to have some control over behaviour of the PF members), it is not obvious that conspiracy theories should be banned. In any case, if you have a well defined policy conserning WTC conspiracy, it could be mentioned in the global guidelines as well for clarity. It is easier to find it there than from years old threads.