If it was overbooked those excess passengers weren't on the plane. United wanted to fly 4 of their own employees (who showed up after everyone was boarded and seated) and "asked" for 4 seats from boarded paying customers.

Without the employee passengers they were not overbooked or any overbooked passengers were not on the plane and we're irrelevant to the situation.

I have flown plenty of times with other airlines when they overbooked and asked for volunteers. They do it in the terminal before boarding starts and generally don't have any problem getting someone to take $800 to hang around for the next flight.

In those cases:

1) the terminal attendant can tell you exactly when you'll be able to resume your flight

2) you can know whether or not the delay will have you sleeping in an airport and can negotiate for a hotel if necessary.

In this case no one (and why would they) took them up on a game of $800 flight roulette, so they had security drag a random guy off the plane.

It was ridiculous when they made some kids have a dress code and refused to let them fly.

This, on the other hand, should be illegal.

I initially responded to a comment that said What's really bad is that technically this flight wasn't overbooked at all.

And I made the perhaps inane point that we don't actually know that.

I still haven't decided whether I think the airline should be allowed to deplane a passenger arbitrarily.

I'm sure that they should be allowed to deplane someone that is being disruptive (this passenger was not), so it is a matter of what justifications are acceptable, not a matter of whether they can do it at all.

In the instance of the kids, the kids that were refused an erection were not following the dress code.

/me thinks you have an autocomplete issue.

Overbooking does not include non-paying passengers that were not confirmed before the flight. Those passengers had confirmed seats and boarding passes and were in fact already on the plane (as was their luggage). In my experience - which is limited, but I've flown quite a bit over the years - overbooking always involved other paying passengers, never crew.

There are many mechanisms for crew (and just airline employees in general - think mechanics on an emergency call-out to a remote airfield) to pre-empt paying passengers.

This case was exceptional in that those crew (presumably) showed up to the gate after boarding, but I've watched a set of mechanics walk up to a gate just as it was boarding with "must fly" company tickets and some of the last folks who had yet to board got denied.

I don't think there is a significant difference in calling this flight overbooked due to the 4 extra seats needed were on company tickets - it just typically happens behind the scenes 99% of the time and is invisible unless you're specifically watching for it.

In the age of social media 'must fly' company tickets are likely to become a thing of the past. As is offering minimum compensation and if not accepted forcibly 'volunteering' a couple of passengers. Spectacles like this are the last thing any public facing company can get away with and if they got away with it in the past it was only because there weren't any easy avenues for people to hold them accountable.

United seems to be on a roll lately.