Except Reddit moderators deal with these spam issues all the time.
Hacker News is run by herculean efforts by the moderation team here, and I appreciate it. I'm ignorant of what their tools are, but I don't think that scales either. Its good for our community, but Hacker News will never be Reddit or Twitter scale.
Reddit's model is that moderators basically complain to the Admins that tools are insufficient, then admins mostly ignore those complaints. Moderators write bots that automatically surf traffic and try to automate... then the Admins come back and increase the price of API-access by 1000%, and then change the API and overall become hostile to this behavior. This cannot work either.
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At least in Usenet days, we could run our own programs in an open source model for these moderation issues.
I don't think Usenet would work. We need a way to rewind time (Usenet: once you post or once something passes moderation, it is forever more sent to everyone else's inbox). USENET was POP model, to put into email terms... while Reddit is IMAP/JMAP model, where the true state of the information is centralized to the server.
So yes, I agree with you that USENET will fail today. But the nuances of why it will fail are important to understand.
In particular: Reddit was never very good about these moderation issues. But with enough work and grit, the community came together anyway. That's good enough. I expect that USENET's moderation model is sufficient, albeit decades old. Its all the other USENET crap that won't work today (being a "POP"-like message distribution platform without any "takebacks", so no editing posts, no deleting porn that got past the spam filter, etc. etc.)
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Or maybe... USENET works with regards to API access. The *ARCHIVE* (ie: Google Groups, or Deja News if you're old enough to remember that) is where takebacks / edits can live instead.
So maybe Usenet can work, but with changes to our workflow to be more akin to 2023-level of features. By separating concerns over USENET (ie: how messages are distributed among a decentralized list of servers), and "The Archive" (which needs to be run by a trusted set of administrators), and a system where moderators will have access to "The Archive" for their own moderation purposes, we can rebuild Reddit through USENET??
Hmmm... it could work. Though I'm curious if it has much benefits over Mastodon or other solutions available today.