United handled this badly, but this is will soon be forgotten by the majority of travelers.
I am a little curious about your protest party's. Do the 85006 look at protesting as a social function? Do they have a committe to chose what the next protest is going to be for? Do they sell T shirts proclaiming their zip code?
There are clauses in that contract, that are federally regulated rules (getting the flight crew to their plane to not delay air traffic). They enforced the contract, via a clause they have a legal argument and responsibility to use. If they didn't, and they delayed too long, then they are in violation of federal law.
And as this article points out, the rules for bumping a passenger PRIOr TO BOARDING are dufferent from the rules allowing them to deplane someone who has legitimately been boarded. Untied appears to have breached their own toghtly worded contract of carriage when they did this.