Just think about how much more persuasive fighting dirty sounds if the whole fate of the human race hangs in the balance. As is, there is an underlying assumption that we have infinite time to grind down our opposition with passive logical superiority.
If the fate of the whole human race hangs in the balance, then it is particularly important that the correct decision is taken, not just the one most driven by tribal feeling, loose rhetoric, etc. Therefore it is particularly important that we are able to evaluate all ideas as accurately as we can, and particularly important not to spread lies, etc.
Of course, if you assume going in that your ideas are infallible, then fighting dirty can look appealing. But if the fate of the human race hangs in the balance, then you can afford the luxury of that assumption.
Scott, known on LessWrong as Yvain, recently wrote a post complaining about an inaccurate rape statistic.
Arthur Chu, who is notable for winning money on Jeopardy recently, argued against Scott's stance that we should be honest in arguments in a comment thread on Jeff Kaufman's Facebook profile, which can be read here.
Scott just responded here, with a number of points relevant to the topic of rationalist communities.
I am interested in what LW thinks of this.
Obviously, at some point being polite in our arguments is silly. I'd be interested in people's opinions of how dire the real world consequences have to be before it's worthwhile debating dishonestly.