Any ideas on how concepts of identity, administration, and content ownership work in networks like this? Who decides to delete an inflammatory piece of content

Any ideas on how concepts of identity, administration, and content ownership work in networks like this? Who decides to delete an inflammatory piece of content in a completely decentralized system? Can a fate like that which befell Usenet be avoided? I could suppose a system where identities are pinned to a key that is stored from the first time the user is identified (because a "packet" is seen from them). But how does that stop a determined attacker from broadcasting out his fake Alice identity, so that the real Alice can no longer spread their messages?