So you would sue an airline if they cancel a flight? That would also be a situation where you are sold a seat but aren’t given what you were sold.
The situation of involuntarily removing paid ticket holders from a flight should be extremely rare. In this case, I don’t think enough was done to entice volunteers. If $800 wasn’t enough to get volunteers, more should have been offered. And then there’s the matter of the four United employees who had to be in Louisville to crew another flight. Why wasn’t this foreseen and dealt with? What sort of emergency was going on there?
My point was that if circumstances are such that people have to get kicked off a plane, and all measures to avoid this situation have been exhausted, passengers should NOT be chosen randomly for this.