This, an incidents like it, beg the question of where we draw the line between (a) personal freedoms (whether protected by government or not!) and (b) the comfort and safety of others.
The argument for this is simple - he would be unnecessarily upsetting customers on the plane. United probably wants to avoid upsetting (paying) customers, since business is already way down. So I can see them asking him to keep the book stowed during his flight, to not upset anyone. However, security determined (on the spot!) that the book itself, as was the passenger and his entire cargo, was harmless. Plus, there's no policy that I'm aware of that says someone can't read certain books on flights because they might upset people nearby. I mean, if I pulled out a copy of Steven Levy's Hackers: Heroes of the Computer Revolution, someone might say that hackers are terrorists, and be upset by it. But would I get kicked off the plane, probably not. Probably, the customer in question would either shut up, or if he persisted, be told to shut up, and I would put the book away for the remainder of the flight. This is common sense, and the best way to diffuse social problems, IMO. It's also what millions of people do every day when they see something that upsets them...
Now, virtually every corporation has a clause that basically says "we have the right to refuse sale to anyone"... and I doubt United is excempt from that - my greyhound bus tickets that I got a few months ago say the same thing, as do the movie theatres, etc. This is basically a "the constitution does not apply here" legal statement. And it is true - private property, the owner can ask you to leave for any or no reason.
So I'm split here. On one hand, United definately made a bad judgement call - and it is not morally defensible. But yet, you really don't have many alternatives to a lot of economic goods that businesses sell. In an ideal world, you could just get a refund and take another flight, but due to monopolies and economic circumstance, that often is either a poor option, or a non-option. United may have been the only option for this kid (or other options may have been prohibitively expensive). On the other hand, going after United would directly impact my rights as a private citizen, and that of other law-abiding businesses engaged in legal commerce. I should always, always, have the right to kick someone out of a place I own, or deny them business. If I don't want to sell my car to someone (for any reason), I shouldn't have to. I fail to see how we could morally justify holding a business to a different standard.
So really, my stance on this is... "Bad United, but what can you do?" It seems any move you would make against them would be an attack on freedom... simultaniously, they have already attacked freedom! The only option that an ardent capitalist would support would be a boycott of United, or a letter-writing campaign, to provide economic incentive for companies to keep certain rights. But the problem with that is that people in a capitalistic economic are self-centered and greedy (Ayn Rand and his theory of objectivism goes into this in some detail), and unlikely to organize for political cause. It's viewed as autonomous to the system - and therefore irrelevant. There's no mechanism built into our economy to encourage/force people to be political, in fact, it's often discouraged. So the only remaining option, really, is government involvement which, ironically, is the very thing that the constitution protects against!
So what's a concerned citizen to do, eh?
Society needs therapy. It's having
trouble accepting itself.