Some things should be deleted because they are bad for the community as a whole. Harassment, threats, doxxing, calls for violence. You honestly wouldn’t want someone to delete a post with “@[email protected] lives at XXX. Let’s get together and beat him to death”? And if that doesn’t faze you I can tell you that most people are not like that. So the place you are imagining would be a very small community very fast. Apart from that there is the problem of illegal content and defederation.