I also have an objective. My objective is this: At least somewhere on the internet, there should exist a community where people can have real discussion, ie, a dispassionate exchange of priors, likelihood ratios and arguments. It will not be possible for me to achieve my objective if participants turn discussions into wars. It will also not work if people with certain views feel unwelcome, or scared to vocalize their views.

Yes, he may have been acting rationally, in the same way that somebody who defects in Prisoner's Dilemma acts rationally. In fact, it would be rational for anyone to use unacceptable tactics in order for their side to "win" the discussion. However, the continued existence of Less Wrong as a rationalist community depends on people cooperating in this game. Moloch will certainly kill the rationalist spirit if we don't punish defectors.

Sometimes it is rational to punish defectors even if the defectors themselves are acting rationally. I do however understand that this is a difficult trade-off, as we have seen strong evidence that there are people who are willing to participate and have high-quality insights that are not easily obtained elsewhere, but who refuse to play by the rules.