To be fair, there has never been a lot of utility in you as a human being involved, theoretically speaking. The users do not use a forum because you, a human, are pulling knobs and turning levers somewhere behind a meaningless digital profile. Any human involvement that has been required for the software to function is merely an implementation detail. The harsh reality, as software developers continually need to be reminded of, is that users really don't care about how the software works under the hood!
For today, a human posting AI-generated content to a forum is still providing all the other necessary functions required, like curation and moderation. That is just as important and the content itself, but something AI is still not very good at. A low-value poster may not put much care into that, granted, but "slop" would be dealt with the same way regardless of whether it was generated by AI or hand written by a person. The source of content is ultimately immaterial.
Once AI gets good, we'll all jump to AI-driven forums anyway, so those who embrace it now will be more likely to stave off the Digg/Slashdot future.