Which just means you don't build the features that are spammable: you end up with friends lists (where users have moderated their own feeds by choosing who to follow) but no discovery (which is where a lot of the dangerous stuff is coming from anyway; good riddance) and no ability to message people who don't follow you (which is the default these days anyway as frankly it is already mostly spam). This sound a like a better world, not a worse world.