I find it to not be acceptable if AI's trend is to degrade performance of both AI and humans at the same time, that's kinda not the goal, right? Why are we spending money to make us dumber?

AI isn't going to go away, and AI-generated content isn't going to go away. So while it's an open question the extent to which AI training will be hampered by the proliferation of AI-generated content, I think that the existence of such content is a reality that we'll have to accept, whether you like it or not.