The AI would not be running the forum. It would be helping running the forum, like an administrator. One that monitors every post and not only stops ones referring to obscenity, fraud, child pornography, harassment, incitement to illegal conduct and imminent lawless action, true threats, and commercial speech such as advertising, copyright or patent rights. It would also look for certain sentence structures that would imply one of the aforementioned items. An administrator that would never get angry, insulted, or go on a power trip. The other admins would of course be monitoring and adjusting if needed.