Most of the things you made mention of here are quite normal and occur most times but you seldom see people quote AI here. If we fully allow the use of AI that it becomes a normal thing then post quality will drop drastically because the contemplation would be , why waste time on research when I can just ask an AI and then paste it here in quotes.
The idea of using AI too much is more like a plagiarism issue because in the end no matter how much you try to put it you are still copying a text or idea that isn't yours.
Adding a good AI to sources for your research is fine since you will actually gather information from different places then drop an authentic post based on what you gather rather than just quoting to post. It will promote low quality posts......
To an extend I go with the Op with the quest of using AI as alternative source of obtaining informations to be used on the forum. It'd had be harmful if quoted because it'd be obviously quoted that the information was generated through the use of AI's. That means users wouldn't be in claim that the post was a humanitized one. Also, it should be rate as same as when we source and quote informations from other internet places or the social networks.
But if considered a deep thought, just as you've said, it's going to be discouraging of users not building that highly classic critical mindsets in going on self research and the attributes of technical self reliance to be creative without the use of the AI.
Moreover, once user is addicted to the use of AI would become a diminishing era of humans qualities in the forum and as well will affect newbies at most because they'd become as lazy as just not to be mentally stressed at necessary human self possessions not just going to be about the forum but also in the reality world.
We can imagine if this use of AI as proposed in the forum is permitted in the schools, I guess that'd really breed dump heads of schoollars which is equivalent to the effect of users in the forum.