Everyone has more authority over their mailbox than any sender. Hence local spam filters block a lot of content without bring censorship. People can share their findings about the patterns of spam, hence collaborative / federated spam rejection lists. They are not dominated by any single entity or a small clique, and every user is free to heed or ignore any part of the list, or none at all. Hence it's not censorship.

This mechanisms formed in the email network long before the current oligopoly formed, and still works.

So I hope there is a honest way to filter out generally objectionable content by.a collective effort of the users who care, without turning the filter into a censorship tool.