Say person A has instance A, and person B is in instance M. Person B mostly enjoys person A, even if sometimes A shares less accepted stuff.
Admin of M blocks A, and person A is blocked for person B too.
Without warning, or recourse.
Person A suddenly dropped out of the universe.
Only solution is an unmanageable 1-to-1 user/instance.
Companies are way worse, but Stalin isn't good because there was Hitler.
This feels very troubling to me.