But by taking money in exchange for a transaction that persists on a blockchain that separates OpenSea from, say, Pirate Bay. It was free to create an account and upload a torrent file and then the sharing occurred off-platform. But since OpenSea operates in the same way as any web 2.0 platform — providing an API that interacts with the thing that does the hosting/sharing — it's more liable to things like copywrite infringement.

I think the analogy with the Pirate Bay actually holds up pretty well. In the end bidding on Open Sea results in a contract method being called on the blockchain which transfers the actual ownership.

Sure, just like the music/film industry targetted Pirate Bay as a central place for sharing torrent files, the same thing can happen with OpenSea.

The more important point I'm making is that the fact that anyone can deploy their own EIP-721 contract means that there has to be central agreement about which is the legitimate version of an NFT. I find this to be an amusing property for a, supposedly, decentralised system.