Not to belittle the problem of spam, but spam isn’t really what people are increasingly taking issue with. “Political” moderation or just plain obstinance are the biggest shortcomings of present day moderation policies. It leads to de facto namesquatting of popular topics the moderators of which have unfettered power to control the narrative surrounding it.
I bet fame and karma points could counteract the disincentives to moderate. What if opting in to a particular moderator translated into 1 karma point per week for that moderator? Moderators of popular topics (e.g. topics with 100k+ subscriber counts) would quickly become some of the most highly upvoted users on the site.
And if commenters could “layer” opt-in moderation policies one on top of the other, moderators could specialize then. Much of the specialization could be done by bots. Anti-“flagrant spam” policies would be easy to bot and easy to combine. The moderation policies left to be done by hand would largely amount to narrative control.
> And of course you need a default for people who have just arrived at the site, so that they're not buried in spam or attacked by trolls on their first post.
That choice could be left up to GUI frontend maintainers, assuming the site itself were open source.
Really I just think social bookmarking has the clearest signal for human communications in general, by far — by leaps and bounds in fact. It’s a public service for such a thing to exist in modern pop culture.