Rational or not, in the US, we have placed upon our officers the burden of having a reasonable suspicion (one that can be later explained to a court) before requiring
anything of a detained person.
As such, if I am a U.S. citizen, and say so, the burden is then upon the officer to identify a reason to suspect that I am not actually a citizen before requiring that I submit to additional questioning or produce documentation. We desire that our cops be required to have an actual reason before hassling us. That form of behavior was what goaded our forebears into shooting at the king's men.
At the risk of inciting an opinionated pissing contest, I'd say that meekly presenting your official papers to a government authority is reason to suspect that you are not an American, and that loudly arguing with the officer (especially when relying on spurious legal grounds) is almost as good as stapling a notarized copy of your birth certificate to your forehead.
I think a simple majority of Americans would probably prefer the government to treat the public more respectfully and courteously--citizens or not--even if it means some dangerous people will find it easier to commit crimes. I may be mistaken in this perception, but I wish for it to be true. It's a crying shame that people are deciding not to visit because our government is acting like a paranoid brute and that I can't find any rational grounds to disagree with their decisions to stay away.