Everything that happens in a US airport is under duress

One, not a US thing. Two, the US Constitution is, despite the hyperbole.

Ignorance is bliss. Americans know because we can access our US court decisions, unlike any other country in the world. (Thanks be to CourtListener and other predecessors.) The "North Koreans have more rights, look it's right there in black letter law" is laughable, despite being repeated nonstop by cough some sectors of society cough since Soviet times.

Here is an old article talking about this topic. Maybe old but seems relevant.

https://www.cbsnews.com/news/us-airports-a-constitutional-tw...

I believe this is correct, but at the airport you're really faced with the reality of the situation. Everywhere else, the same mechanisms exist 'under the sheets', but there's a thin veneer of society pasted over the machine.

how

I don't suppose you've actually, you know, read the constitution? If so, I'd be fascinated to hear about which parts pertain to, or don't apply at airports that should?

The main thing people seem to find difficult to comprehend is that planes owned by airlines are the private property of the airline. You're pretty much welcome to buy your own plane, and use it to carry anyone and anything you want, but if you want to get on someone else's airplane, no so much.