Not so infrequent if anyone could board with their favourite pistol, I suppose machine guns would have to be allowed too and that would mean several of those windows could get broken at the same time.
If someone had a gun, but nobody knew it, then it really doesn't matter, I don't care what someone has in his pocket. I think people carrying concealed weapons do have a different mentality. If a perceived threat induces them to arm themselves, they are more affraid, perhaps a bit paranoid, likely they draw courage from the fact they are secretely armed. I suppose there are 'normal' people who carry concealed weapons, they derive pleasure in secretely knowing they are fully exercising their constitutional right, and ready to spring into action if anyone gets out of hand.
Its hard to iamgine the sort of people who would carefuly conceal a weapon as they get ready for church on sunday, to watch the kids in a school play or off deal with some government bureaucrat... What's the gun for? Just in case? In case of what?
I'm glad I can argue about this online with people like Apeman, because if we were discussing it over beers at the local somewhere in Arizona, I could provoke him too much and get shot.