People should related to anything federated like email. If you send something it is in someone else's computer now. With matrix or any e2ee protocols it is depending on pinky promise of the client to modify it. I thought the whole Snapchat fiasco already taught us that. Did we forget?
There are many cases in between, though, in particular those where you're using messaging for "serious" purposes like business, but not so serious that the other users are your enemies. Sometimes for instance you want to let people edit/delete recent messages but not really old ones (to prevent someone trying to "rewrite history").
There's a difference between "I have an active adversarial actor" as a security model and "sometimes I send something I don't want to and want to delete it, the people watching are friends and acquaintances and are not deliberately preprepared to collect kompromat".
When I delete a message off Signal chat, the expectation is that the chat members are agreeing by social contract to abide by that.