the forums I'm familiar with have a ticket approval flow for new accounts too. sometimes you need to know a current member etc

not so easy to do at scale or agentically, although you can babysit your way past that probably

Some of them are doing that, but they are either not getting many members (not always a bad thing), or they accept everyone who can act human (which a LLM can do close enough). Sometimes there is a probation period, but it wouldn't be hard for LLMs to write enough to seem real.