This falls apart with any comparison with email. Email is a pure push protocol that assumes all actors are trustworthy. Messaging in the vein of ActivityPub, is

This falls apart with any comparison with email. Email is a pure push protocol that assumes all actors are trustworthy. Messaging in the vein of ActivityPub, is pull: you might be able to opt in to receiving messages from anyone, but you don't have to. You can subscribe to people and only get messages from them and those they boost. And you see who's boosting stuff you don't want to see and can stop following them or talk to them. That reduces the problem down to a narrower set of social problems, and social issues are hard, but in a different way: you've just discovered your friend is a jerk rather than them being an open relay.