Each shard of encrypted with a unique key. So if you wanted to make a decentralized cats website, you would publicly post the locations and decryption keys for each of the shards. Of course the application would take care of this all behind the scenes, and you would just have a website that you could scroll though cat pictures.
Now if the farmer hosting that data find out they are hosting public data, I don’t really see that as much of an issue. I’m assuming you are pointing toward an edge case in the fictional country of Dogtopia, where cat pictures are illegal. The farmer would be covered under SAFE harbor like provisions in more civilized countries, and only storing an encrypted piece of an “illegal” file could question if you are storing the file at all.
This is where greylist comes into play. Curators create a greylist with all the ids for the publicly available cat pictures. The farmer that lives in Dogtopia they can opt-in to the greylist, and it will automatically remove those shards. Obviously anyone outside of Dogtopia would not use that greylist.
tldr; Private data stays private. For public data the users get to choose according to their own morals and laws.
Additional points:
- To prevent abuse greylists are open and forkable.
- Just because content is on a greylist doesn’t mean it gets removed from the network (that would be censorship). Contract would be renegotiated with another farmer.