I've got a question: to what extent can they dish up the "Terms of Service" argument? That is, can they refuse to fly you (domestic) if you refuse to comply because it's a "term of service"?

Is there any niddling contract law in purchasing plane tickets?

Isn't the argument that every international airport constitutes a border, and every mile of beach, and every mile of an actual border? That zone covers the majority of the population of the US constantly.

Don't you mean any area within 100 miles of the borders? That means some states are completely within this region and are all subject to border searches.

I would love to see the government attempt to defend such a stance in front of the supreme court. I have a sneaking suspicion there'd be a major judicial shitfit on that.

Chief Justice would probably be all: "LOL, you did wut? ಠ_ಠ"

The problem is that they don't have to (yet). They do it now and get away with it and currently with impunity. If I recall correctly, there is a case in Texas about the matter, but that is the only one I know of at the moment.

This is a concern, yes.