I see maybe, I misunderstood. So do you mean whitelisting messages (tweets, posts, any other atomic units) based on content? I think white listing based on content may be hard, especially say images or videos, in a decentralized network. So I thought you mean whitelisting based on identity/id which is useless in mostly-anonymous permissionless network.

(But actually content-based filtering may not be too impossible now that I think..)