How does this stop people from posting nefarious content? What's to stop a group of bad actors setting up a group accessible only to those that have a certain trait and then using it to exploit people? E.g. trafficking of peoples
Plebbit uses IPFS. What should stop them is that IPFS is not private at all, it's just like BitTorrent. ISPs, copyright trolls, government agencies can all track the swarm and log your IP address in it. As it's often done with torrents, you can use Plebbit with a VPN to hide your IP address to everyone except the VPN provider itself, who you are trusting with your entire network activity. The most privacy-preserving way to use Plebbit (or BitTorrent) is probably to use it with a VPS you paid with Monero, via Tor; in this case, what would enable the exploitation is Tor and Monero, not Plebbit.