If the goal is victory for our cause, and not just victory for some people who find it convenient to claim to be cheerleaders for our cause, we need to be very careful that our tactics are not training up Stalins within our ranks.
Well said. Also, an additional benefit of rational discussion is that it promotes truthseeking - people may discover that the cause that they're supporting is not the cause that they should be supporting. Under a "win at all costs" paradigm, arguments against your position are enemy soldiers, so if you win, it'll be without seriously considering the arguments of the opposition. That increases the likelihood of you being wrong. If your goal is something beyond personal power - if it's something like "the correct thing should win and become dominant" and not "I, as I am now, should win and become dominant" - then honest discussion is even more useful.
Also, as I mentioned here even if your initial cause was right, by lying about it you'll attract people who believe your lies. Thus, eventually your cause is likely to morph into something that is a bad idea.
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.