I don't think you're correctly using the phrase "karma sinks." Or at least, you're not using it the way I see it is typically used on LW. Karma sinks refer to comments users make in order for other commentators to purposefully downvote if they upvoted another specific comment. This is so we can do things like straw polls without the polling user gaining tens or hundreds of karma.

That might be unclear, so I'll give an example. I recently made a comment asking whether people would be interested in a New Jersey meetup. I could have also asked those interested to upvote my comment so I could have a rough estimate of how many people are interested. As per community norms, I would also make a second comment for users to downvote if and only if they upvoted the first comment. This second post (the karma sink) would help assure my net gain is 0.

Anyway, that doesn't invalidate your point. But for clearer communication, you may want to use a phrase like "positive feedback loop." That seems to better describe what you're talking about, where downvotes make it more likely that other users will also downvote, which in turn leads to even more downvotes, and so on.

Rude things aren't inherently unproductive.

They are, in part because they predictably make people behave less rationally.

And 1/3 negative karma means that we would get rid of many productive things

I don't agree with your implicit estimate that less than 1/3 of the comments here are net negative contributions. Still, noise would indicate that your conclusion is correct - I'd expect even now some large amount of productive things are hidden from view.

so more downvoting is still an awful idea.

That does not follow (that you thought it followed is indicated by your use of "so"). If you wanted that to follow, you would have to also establish that people here actually do downvote at least 1/3 of the comments here, which is clearly false - even I don't downvote that much.

I assert that people are extremely stingy with their downvotes.

You're also completely shifting the Reddit thing from what you initially said it was supposed to show, from "curation key to stop LessWrong to becoming Reddit" to "it shows why curation is important", where the reason it was important was "because it stops Reddit" but yet you conceded that the reason it's important is not "because it stops Reddit", there's an implicit contradiction.

I'm confused. Where did I assert that "because it stops Reddit" (in shorthand) is not a reason that curation is important?

Karma sinks are where people are more likely to downvote things that have been downvoted.

More likely than what?

I would expect that people are more likely to downvote things that have been downvoted, than things that haven't been, since things that have been downvoted are generally more downvote-worthy.

since my account is already ruined, by continuing to bump this comment thread I can wage a war of attrition against you. there is no real impact to my receiving more negative karma although there is a high probability. conversely, there is a small probability that you'll receive some negative reputation (or even better, this part would all be deleted) and there is also an impact to your credibility.

You overstate the degree of ruination of your account and so I don't quite support the details of your reasoning. Nevertheless, drethelin has something to learn from this. He gave you a lot of power over him. That's usually a mistake.

mostly this post is just me being frustrated though. i feel like lots of the other comments in this area were like your above comment, except that other people were less transparent about it

Pretty much, yes. I think they call those 'social skills'. Actually, drethelin is more or less following your no-politeness policy perfectly. Sometimes that is actually more pleasant to be on the receiving end of than the well crafted socially acceptable salvos.