“How is it that if you arrive at JFK Airport without a passport, you are sent back to your place of origin, whereas if you cross the Rio Grande River without a passport, you are not sent back?”
I can only assume that the same is true if you were to arrive at Chicago O'Hare, or Sea-Tac, or LAX. The only conclusion that I can come up with is that those cities are full of racist, hateful, intolerant people.
Well, they are. I've been there.