Simple conclusion not yet stated
Still reading the backlog but amazed at the lack of critical reasoning of the many who have argued that a two person cockpit rule is a knee jerk response and not guaranteed to prevent a repeat. Of course not guaranteed but consider this simple, obvious but (so far not stated) conclusion that can be made if a two person cockpit rule had been applied - at the moment the captain left the cockpit, the FO was in SOLE control of the aircraft. If a FA or any person had been substituted for the absent captain, the FO would NOT have had SOLE control and would have had to overpower the substitute by force or persuasion to prevent him/her opening the door to the returning captain.