> If you no longer have access to your phone, you should have to contact Apple support or go to an Apple store.

Requiring users to visit an Apple store to leave Apple's messaging ecosystem doesn't seem like an ideal solution, to put it lightly.

I think the status quo is actually not terrible, and with a simple modification (making any externally-triggered deactivation very visible on the logged-out device) it could be secure as well as being usable.