I’ve heard that only a “good guy with a gun” can stop a “bad guy with gun.”
There are some problems with this argument.
1) In Dallas recently there were dozens of police officers with guns along a peaceful demonstration route. They were the good guys with guns. Five of those good guys with guns died and several others were injured by the hand of one bad guy with a gun.
2) It took a robot and a bomb to stop the one bad guy with a gun. A robot and a bomb — not a good guy with a gun.
3) One of the protesters was an open carry enthusiast who was considered and publicly identified as a suspect; he did turn his gun in to police. This clearly shows that the police could not tell if he was a “good guy with a gun” or a “bad guy with a gun.”
4) Neither the suspected open carry activist nor any of the other open carry activists at the demonstration took any action against the bad guy, although they all had guns. What’s the point of being a “good guy” who carries a gun if you aren’t going to use it on a “bad guy”?
And finally:
5) Every “bad guy with a gun” and every “good guy with a gun” are completely indistinguishable from each other; it is impossible to tell the “good guy” from the “bad guy” — until the bad guy starts shooting innocent people.