>I don't think there ever will be. I would probably not shoot a kid that I only suspect would shoot someone. I doubt a teacher would either.

There have been interviews with bystanders who had firearms on their person during a mass shooting and they didn't use their firearm because they didn't want the police to think they were on the side of the attacker(s). The idea that life is like a video game where there are unambiguous and easily identified "good guys" and "bad guys" in a chaotic situation is very juvenile.