The commander (captain) of the flight has the authority to off-load passengers if they ......(a repost)
The commander (captain) of the flight has the authority to off-load any passenger if in his professional judgement, threaten the security and safety of the aircraft, the crew and other passengers.
In my 35 years working with the airline, I've come across a few cases of captains booting passengers from their flights.
I remember a passenger demanding an apology from the captain for "loitering" in the cabin with his co-pilot. If no apology was extended, the passenger told the captain a complaint would be filed with the chairman of SIA. The captain refused to apologise and on arrival at Sydney, booted that passenger who was supposed to continue his flight to Melbourne. The captain explained that the passenger had undermined the confidence of fellow passengers in him (the captain) by accusing him and his co-pilot of deserting the cockpit.
There was another case whereby a Caucasian passenger made a derogatory racist comment about the captain. The passenger was off-loaded before the plane took off.
There were also a few cases of the airline blacklisting its passengers.