I don't think posts should be flagged for being AI (they often contain interesting or important ideas as well), but I do think it should be pointed out.
Slop is slop -- if it is AI generated slop then fine, call it out.
If it is not slop what is the point of this compulsion? It derails a lot of threads when the content is actually good.
It's like deepfakes. You only know it's AI when it's not convincing; when the deception has failed. When you're fooled, you don't know it's AI. You just think it's a video.