They teach you this in the course you need to take to concealed carry.
If someone is doing massive damage...cornered people in a restaurant and is shooting them one by one. Someone can respond to that. Youre going to hear it and see it. Not every scenario is going to play out perfectly but at least theres mitigation on the table.
If everyone has a gun, then either you teach this skill to everyone including the bad guys[0], or you don’t teach it to everyone and now a lot of normal people with guns are indistinguishable from bad guys with guns.
[0] because if you actually knew they were bad guys before you gave them such training you could stop them before they fire a single shot
If someone is doing massive damage...cornered people in a restaurant and is shooting them one by one. Someone can respond to that. Youre going to hear it and see it. Not every scenario is going to play out perfectly but at least theres mitigation on the table.