Critically, Slashdot also had a meta-moderation system, where users were asked to judge moderation activity to confirm whether it was sensible, fair, and so on. I'd like to believe that system played a vital role in stopping abuse of the moderation system. It was way ahead of its time.

I've been advocating for a while now that HN could use meta-moderation at least on flagging activity, so it can stop giving flagging powers to users who are using it for reasons other than flagging rulebreaking.