But then, on top of running a free open relay, you are running a free moderation engine. Who will pay this? 

I see this as an identity problem in general rather than a Nostr relay problem. If you can ban an npub, that person can create another one. We need to ban the person or an AI that's posting. 

Worldcoin offers a solution to scan all the unique humans on Earth to solve this problem along with the human vs AI problem. But there are 8 billion people on earth. And Worldcoin accounts are as cheap as $20. It doesn't solve the identity problem in my opinion. Plus, not everyone will scan their eyeballs. 

I think we should identify people based on the most scarce possession on Earth. Bitcoin. 

I want to propose "Proof of Bitcoin". If you ban a  Bitcoin balance, its much much harder for a scammer or an illegal content poster to save enough bitcoin to post again. 

What do you guys think?