The U.S. deregulated the airline industry back in the '90's. Until then it wasn't allowed to overbook a plane. Since then it is. The airlines decided to overbook (sell more tickets than there is seats) to compensate for people that buy a ticket and don't show up, and then re-book later using their credit with the air line.
They overbook in an attempt to fill up the plane and maximize profits. When everybody shows up, somebody gets bumped. They usually offer a "travel voucher" or cash for someone to voluntarily give up their seat, and that person takes a later flight and has the voucher or cash as compensation for being inconvienced.
when no one volunteers, then someone gets bumped involuntarily.
Where it gets $hitty is that it's not always the last guy on the plane who has to leave. Let's say you fly once a year and got your ticket at some last minute flight discounter for $200. And there's another guy without a seat who flys 5 times a month with the same airline and paid $800 for his ticket at the counter an hour before the flight. Guess who's gonna get bumped.
The airlines make the decision based on a business decision. The frequent business traveller gets the seat.
Is is it fair? Nope. Does it suck for the guy who gets involuntarily bumped? Yup. But those are the facts on how the airlines work, and right in the fine print it stipulates how and why the airline can deny you service. And make no mistake about it they can deny you service whether you think it's your "right" or not. The airlines routinely overbook and then have police escort people off who refuse to leave. The incident the other day is what happens when a bunch of people make bad decisions and don't think things through.
This united airlines fiasco was because of a deadhead flight. I agree with everything you said... But they booted him off to make room for another flight crew.