You don't have unregulated "perfectly legal speech" on Hacker News; posts can be downvoted until they disappear at the whim of users. That doesn't seem to have

You don't have unregulated "perfectly legal speech" on Hacker News; posts can be downvoted until they disappear at the whim of users. That doesn't seem to have doomed the platform. Too much toxic content and spam, and I think there's a big overlap between the two, will make a platform unusable or at least undesirable to many. That's what happened to Usenet.