Being born in the USA, I have a quaint attachment to the ideals of human dignity enshrined in the Constitution and Bill of Rights and it grieves me deeply when officialdom and their minions disregard these ideals.
Four or seven hours confinement in a full plane after 12 hours in flight is a lousy way to treat people.
Airports seeking diverts should have facilities for uncleared pax and a contingency plan for looking after them.
HS rules should facilitate doing the right thing for the pax.
Admittedly Canada confined dozens of flights full of pax on 9/11, but I suspect that an early stop in YEG, YYC, YWG would have kept the crew within limits.
It would have even been possible to process the pax through US customs and immigration at any of these airports and they could have been bussed from GCIA -- the driving time is less than 3 hours.