I have an uncomfortable feeling that's the entire point of this exercise, though :-(. We've already had one thread closed because "The valuable posts in this thread occurred in the first three pages, the quality of posts have declined since.", where not valuable seems to mean posts questioning MagicalTux's story. Meanwhile other users have got away with tediously repetitive claims that the person whose 500,000-bitcoins were sold must've been plotting to undermine the market, copy-and-pasted multiple times in bright colours in the same thread.

There's no constitutional requirement for free speech in forums, but the principles are still important in some form if you want a workable forum. While forum moderators may technically have the right to moderate arbitrarily, it's basically impossible to have a meaningful discussion or trust the forum threads to actually represent the opinions of the users in any way whatsoever if they abuse this. Worse still it's impossible to tell when they are abusing it as an outsider, so at the slightest whiff of dubious moderation you basically have to assume all discussions are tainted.