email and irc are both federated services and users depend on their server software or server admin to make sure weird content does reach them. In an actually decentralised system you must expect the client or protocol to deal with this.
IRC is admittedly not the best example since you can't usually join an IRC network "swarm" without approval.
I think email works though, anybody can spawn a postfix server and interact with the rest of the mesh immediately. I run my own email server that I fully control and I never had to ask anybody permission to do it.
I think it would make sense for Radicle to work somewhat similarly, anybody can spawn a repo, there's no central authority that can censor or alter any repo but the owner still has full control over it.
