Moderation systems, even with humans at the helm, are adversarial systems where people can, and will, push on what is allowed. An AI moderator that is as good as a human on a per message basis is still going to be played like a fiddle by an adversary that is interested enough.
Many a forum out there has collapsed because the moderators manage to decide something is fine when it keep losing them contributors. The why do we think the AI will do better?