Well, good on him and I think you are verballing him with that last bit. Presumably it'll take a bit longer to board and cost a bit operationally to make absolutely certain no-one gets on board who can't be flown, but we'll probably be the better for it.
But other than that, the comment is irrelevant. You have contended that, in the event of an on-board disagreement between a pax and crew on some instruction, there should be a commercial discussion until there is an agreed outcome. I'm contending that that's unworkable, and will lead to anarchy, as inevitably some pax will try to exploit the 'kinder, gentler' approach for unreasonable gain, and once one pax gets close to being unreasonably 'bought off', others may follow, and you'll get an on-board 'Mexican Stand-off'.
Then what? What do you think the new United manual will say about this situation?
'This' being everyone gets de-boarded in the event that a passenger can't be satisfied and the airline can't forcibly remove them.
Well, I'll bet airlines have thought of it (and there are stories that the Dao aircraft WAS totally de-boarded, before being re-boarded and operated), however because they were previously allowed the latitude of acting unreasonably and using or threatening 'security' in inappropriate situations, they haven't had to use it.
But again, lets have a think. If a passenger gets on board, and acts unreasonably but not in a threatening situation, and there is no imperative to obey a crew instruction, merely to have a discussion until agreement is reached, and they can't be forced off ... what happens?