Any one comment is not harmful. There are tons of those in LW already on the -2 to +2 range. What's harmful is all of them put together. The response is to either not have huge surges, or to collectively fight the surge by collectively imposing higher standards and voting much more actively.
And as with collective solutions, there are problems with defection... No individual benefits much from going through a new page and up or downvoting each comment. To quote Buffet, I think:
"Overall, however, we've done better by avoiding dragons than by slaying them."
It isn't obvious to me that additional clueless comments are superlinearly harmful, that their harm outweighs the benefits of greater publicity, or that the problems with defection that you mention are serious enough to prevent a collective solution from working.
Recently reporters from two major national magazines contacted me in preparation for doing stories on Bitcoin. This reminded me that Wired magazine did a cover story on the Cypherpunks in its second issue. I think the LessWrong community is already larger and more active than Cypherpunks were back then, and potentially more influential, but there hasn't been much publicity on us. I'm tempted to suggest doing a story on LessWrong to one of the reporters. Is this a good idea, or bad?
More generally, do we want more publicity, and if so what's the best way to go about getting it?
ETA: Would it be bad etiquette to reveal the names of these magazines at this point, or even to say as much as I've said?