Answer: Because they did not realize the rules and regulations in place. The person in my example simply turned around to go make amends, and ends up getting arrested and charged depending on what he was carrying that made him decide to turn around and go fix the problem.
"It really isn't that hard to avoid arrest at an airport checkpoint. And it doesn't require someone to be an absolute genius, or to know every jot and tittle of the law."
I agree. But it can and does happen. We have become a nation of criminals just by going about our daily business. People every day in America overlook and/or forget about all sorts of laws that have nothing to do with protecting the rights of citizens. I can't even fill out my own income tax return without violating some law. I have to pay a professional. Even then, he gets it wrong occasionally.
This person in my example never harmed anyone or intended to, and will likely become a criminal because he was unwary of some stupid federal laws, that in my opinion are ineffective as well.
Speak for yourself.