PDR1
Your post shows you know the contracts that airlines issue and the leagal issues surrounding them, but it also shows that you have now idea of the of the dynamic of the disruptive passenger issue as it unfolds in the air.
The theory that you speak of retreats to the back of your mind as the the cabin crew are being assaulted and the normally law abiding passengers becoming involved as they try to defend family members as there is no chance to run away on an aircraft, add to this a little fear of flying that a lot of passengers have and the mix that is toxic. When the the situation starts moving this way the only place to be is on the ground with the help of the police.