So, I think, if we don't want to see the forum turn into a place full of AI-generated content, we need a rule that would get users banned, first temporrily, and then permanent for repeated offenses. Also, some will say it's not easy to always identify AI-generated content, but, whenever it's done, as we can see in the thread I mentioned above, at least then some action should be taken.

I totally agree with the spirit of your post. The only difference is how hard you want to go against AI garbage, and it is just a matter of technicalities. The hidden idea (more of a concern) behind OP is 'it is getting very difficult to differentiate between AI and human and things are only going to get worse'.I mean, this is the ultimate goal of any AI, think and act like a human(ideal). What about people who will learn everything from the internet? Which will be 90% synthetic data? They will start copying AI style as standard, imagine the mess.
I am sure that many senior quality posters are feeling the need to scan their own original post through AI detectors just to be sure that someone can't intrepret that as AI. This is how ridiculous AI and human differentiation has become, and it is just the beginning. Most senior members here have read actual books and have debated with actual humans and we got to preserve that at any cost. I will not be surprised if tommorow human written text will be more expensive and therofore more rarer, just because of mindless AI outputs.
That's why writing as a conduit of your mind is a much better style that writing correctly.
Many years ago I read a james jocye novel unlesyes [ spelled wrong] said to myself what the fuck is this shit.
And here we are 50 or 55 years later and that stream of consciousness style is very very very good at fighting AI.
My fear of ai is that it gets to the point that it is fully equal to human writing.
There was a short sci fi story of how writers all wrote with ai pcs. And the heros ai was defective or broken so he wrote on his own. He became a hit. It w a s a very good read. And here we are 50 years later and that story looks more and more important.
I WILL TRY TO FIND THAT STORY.