Some myths die hard.
...statistically, it's more likely that someone with a concealed carry permit will set out to commit mass murder than prevent it.
a 2014 study from the University of California–San Francisco found that people who owned a gun were three times as likely to kill themselves as non-firearm owners; by comparison, the annual per capita risk of death during a home invasion is 0.0000002 percent. Hell, even toddlers killed more people than terrorists in 2015. Guns are used far more often for killing than for self-defense, despite the fact that some 63 percent of Americans think guns make them safer.
Only seven of the 160 of the mass shootings that took place between 2000 and 2013 ended because of some would-be Rambo came to the rescue
More than half (56 percent) were terminated by the shooter who either took his or her own life, simply stopped shooting or fled the scene. Another 26 percent ended in the traditional Hollywood-like fashion with the shooter and law enforcement personnel exchanging gunfire and in nearly all of those situations the shooter ended up either wounded or dead. In 13 percent of the shooting situations, the shooter was successfully disarmed and restrained by unarmed civilians, and in 3 percent of the incidents the shooter was confronted by armed civilians, of whom four were on-duty security guards and one person was just your average "good guy" who happened to be carrying a gun.