I think of rudeness in LW discussions as a signal. Broadly speaking, LW commenters are rude when they think they are dealing with a stupid argument, and/or an argument that fails to follow the established rules of rationality. The implication is that they can't be bothered writing a more detached response, and (since rudeness is more likely to drive users off the site) that they would not want to see similar comments in the future.

It strikes me as a useful signal; sometimes more useful than karma points, which can be affected by factional or 'political' considerations. This might be one reason why Crocker's Rules tend to be relatively popular here at LessWrong.

Nonetheless, it might be worthwhile to try and challenge the social norm where users with more status can afford to be more rude. In my view, it would be interesting if some users with high rationality skills were willing to be expressly low status users, or "resident trolls". Their role would include debating with especially irrational, politically-motivated or trollish newcomers. Rudeness on their part would be expressly encouraged; due to their low status, it would hopefully not be seen as threatening the social standing of other LW users.

Ideally, users with the technical ability to delete comments here (most obviously Eliezer) would also take on the low-status, "resident troll" role. This would ensure that such technical measures are only used a last resort, if any attempts at discouraging unproductive commenters by social means failed.