I think the #1 problem that needs to be addressed is how to completely remove content from a blockchain social network. Otherwise it's going to be a permanent record of every mistake someone makes online.
In Farcaster, deletes are possible. They use a hash chain (new messages refer to previous message's content hash). If a user deletes a cast, they delete the content of the message and the hash is no longer correct. This makes deletion both possible and detectable, since users can self-host their messages. Note that in Farcaster only username mappings are on-chain, the rest of the messaging protocol is off-chain.
