Curi's karma has repeatedly dropped low enough that his posting rate is moderated. If that's going to happen then it should occur based on the quality of posts not to him being socially tone-deaf about community norms of where to post things.

That's Curi's decision.

(Incidentally, there's another reason to downvote short link posts and the like in the main section- some people just have the RSS feed for the main posts and don't want every little link to show up).

Okay - a valid reason.

I would still like to say that, when considering whether to impose a social norm against posting certain things on the main page, saying that you think they're unworthy of karma is not a good reason, because (a) karma point accumulation to users beyond getting enough to post does not give them any advantage, and (b) you can choose not to vote, and therefore you can object only because you don't trust the judgement of other users on LW and so would like to deprive them of the freedom to vote for such articles.

This may not have been your reason, but this seemed like a good place to make my point.

Scores in the negative are kept track of despite not being displayed, however. In particular, people with negative karma have a commenting frequency limit, whereas people with zero karma do not.

Scores for total karma are displayed as zero if they are negative. Scores for individual articles can be negative (and in fact it is back to -1). I have various hypotheses about why the score has moved up but I'm waiting to gather more evidence before I state them.