The problem is that how will you proof that a message is AI written or self written ?
There are tools to detect this. You can find them by simple Google search.
But the problem will be of scale. If people start abusing this here or on any other forum, because of the huge volume of spam, it will consume lot of forum staff time to spot and end this. This challenge will be faced by all forum owners in future. One site I can give example of here is Quora which is getting filled with such AI posts.