Being pro-gun does not stop massacres.
Of course it does. If there had been law-abiding, licensed gun carriers at the sites of all these mass shootings, most, or all, of the innocent people killed would still be alive, and the murderer would have been shot on the spot.
Either that or he wouldn't have even showed up, knowing his chances of failure would be high.
Donald Trump and Ben Carson are both right that one of the primary things to blame, is the senseless, idiotic policy of
gun-free zones, which has allowed these shooters to carry out their rampages unhindered.