Just an idle thought
Seattle: "Good guy" with pepper spray stops "bad guy" with gun. Good guy and bad guy both still alive; bad guy being arraigned for trial.
Las Vegas: "Good guy" with gun goes to stop "bad guy" with gun. Good guy and bad guys all dead.
Just a thought, but maybe having a gun is not enough, even after the shooting starts so you know it's a bad guy with a gun and not some open-carry advocate...