I can’t vouch for the veracity of this account, but it has the “feel” of being real. I can very easily understand how a trusted colleague can suddenly become a bit more suspicious-looking if they started openly carrying a gun.
But that trust and faith can return with interest when a real threat materializes. That’s when Bob, the scary guy with the gun, becomes Bob the defender of the innocent.
I don’t have any hard stats on the matter, but it seems to me that most (if not all) of the recent massacres have been committed by people who were not licensed to carry guns, and not with their own registered guns. The Columbine killers stole their guns. I can’t find the links at hand, but I recall reading that the Omaha mall shooter also stole his guns, and the DC snipers stole their rifle. For the most part, the shooting rampages are not carried out by licensed gun-owners with their own guns.
It all boils down to how well do we trust our fellow citizens — or if we would rather disarm the law-abiding ones in the hopes that we’ll also disarm the dangerous ones, who are already set on breaking far more serious laws.