It should certainly be easier and less unpleasant, and less likely to draw expensive lawsuits if people are prevented from boarding the flight in the first place than waiting until they are settled in and ready to go. Getting some money back would be more likely acceptable if one is not yet on the plane. The practice of uprooting people who are already seated is nonsensical. I expect the least polite method to be used at UAL because that attitude seems to be part of their marketing strategy but the other airlines have no excuse.
“It should certainly be easier and less unpleasant, and less likely to draw expensive lawsuits if people are prevented from boarding the flight in the first place “
Right. From the reports I heard, the passengers got approval from the Gate Agent to have the youngster take the seat that was in his older brother’s name — bought and paid for. The Gate Agent said, “Yes”. The PTB said, “We can sell this seat twice and make a little more money!”