What happens in America, influences significantly the rest of the world. Yes. But it's almost orthogonal to the question of how to win the battle within America.
If the hypothesis "if you play nice, you are more likely to win (because people will enjoy joining your side), and if you play dirty, you are more likely to lose (because neutral people will hate you, and you will also have a lot of internal fighting)" is true -- which is the thing being debated -- then the fact that the outcome in America will strongly influence the rest of the world, just makes it more important to play nice in America.
More meta: If you believe some strategy is the winning strategy, increasing stakes should make you follow the strategy more carefully, not abandon it.
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.