What do you mean by "complete pacifism"?
The way to fight someone how spreads lies about you is not to spread lies about them, it's to spread the truth about them.
When I speak of fighting back, I'm talking about making them pay a cost, and not feeling constrained to play fair for their sake. They've forfeited that consideration.
If you have overriding reasons to tell the truth, do so. But not to preserve value for them. When someone attacks you, it's time to destroy values for them.
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.