Airlines are not government entities. If they want you to stand on your head and do push-upin order to board, that's their right.
It probably makes their shareholder happy.
I also rather prefer riding on planes less likely to be attacked by terrorists.
What prevents him from crossing any U.S. state line he d@mn well pleases by automobile, train, motorcycle, boat, horse, foot or pogo stick without showing identification?
You do not have a Constitutional right to travel by air without showing that you are not an individual who may intend to kill every individual on your flight and maybe thousands more on the ground.
The answer is yes. Anyone is subject to interpellation on public property even now. The public agent still needs a court warrant to enter private property. For now.
There's a lot of "show me your papers" folks here who are convinced terrorists can't or won't board airplanes with bogus ID's and papers.
They're a pathetic and silly lot, the whole bunch of them.
Just read their comments justifying the loss of our rights in the name of make believe "security."