JUST ONE EXAMPLE?

Slots Bennett thinks having a lot more people carry a gun will greatly reduce the chance of another massacre but Mother Jones only found one (1) example of that happening:

Bar shooting in Winnemucca, Nevada
In 2008, a gunman who killed two and wounded two others was taken out by another patron in the bar, who was carrying with a valid permit. But this was no regular Joe with a concealed handgun: The vigilante, who was not charged after authorities determined he'd committed a justifiable homicide, was a US Marine.