I feel like twenty odd years ago you can just open the gates to a web community and get by with little moderation; you can still cultivate a community from which participants derive some value. Nowadays, moderation would have to be no less than someone's full-time job. And I believe this has been the case for a good few years #before# generative AI came into the scene. Maybe for a good while you can hold down the fort with technical moderation solutions like fail2ban or Captcha but I bet you will run into problems within your first half a million users or so.
Maybe projects like Mastodon have more robust solutions to this but, still, moderation will be a problem if and when you make it big, just like your server costs.
Finally, don't even get me started about CP, which is a whole other level of low and rotten. Maybe if you restrict your community to niche topics it would (a) deter malicious outsiders and (b) be self-moderating to a degree. The thing is, a niche discussion forum old Facebook ain't.