Not a valid comparison.
A private person (company) owns their property and has the RIGHT to set the terms of sale. In this case, United even though regulated through the DOT did something legal (overbooked the flight) as they have always done. Further, they told PRIOR TO THE SALE, that they overbook their flights and passengers may be required to be involuntarily bumped. The passenger then ACCEPTED the terms of that contract and completed their purchase.
Then they throw a fit when the carrier expects the passenger to ABIDE by that contract.
They DIDN”T OVBERBOOK they were making room for their own employees clearly not the same thing.