[krapp]

Your examples are irrelevant because they're controlled environments - in a gun shop most of the guns are locked up behind bulletproof glass. The police make certain they're the only ones with guns inside a police station. And nobody would be stupid enough to start something in a place where people are practicing shooting targets with already loaded weapons.

The point about the teachers is a good one - though culturally and politically I don't know if that would work very well in the United States. But to be fair to your point, we would have to also allow the students to carry guns to protect themselves against the teachers, who now represent an oppressive and violent arm of the state after all, and we're down to the same problem - how does one tell the difference between a trustworthy, armed person and an untrustworthy armed person?