People who are posting AI comments or setting up AI bots are... people. They can show their ID. If a website owner doesn't have a way to ban that specific human and the bad guy can always get another voucher, it's sort of meaningless.

In fact, even if you can ban the human for life, I'm not sure it solves anything. There are billions of people out there and there's money to be made by monetizing attention. AI-generated content is a way to do that, so there's plenty of takers who don't mind the risk of getting booted from some platform once in a blue moon if it makes them $5k/month without requiring any effort or skill.