I do wish we could discourage the attitude displayed here by gwern. It's pure ego to respond in this way to someone you deem a "troll". It certainly won't change their mind, and it will only spur them to comment more. Either ignore them completely after downvoting, or be polite in your reply. One might justify these posts as important to make sure that 911truther knows why he's being downvoted, but the aggression in them is entirely counter-productive and, frankly, is quite rude.

For the record, I do think people are a little over-eager to accuse someone of being a "troll" (I think it is much more probable that 911truther is simply ignorant) although I think moderation is warranted in this case.