Prior to the modern era, large numbers of people carried guns. They went to stage performances, circuses and so on. How many mass casualty events have been reported in shooting incidents? None that I have seen recorded.
How many incidents of someone opening fire on a crowd with semi-auto weapons are you aware of?
Look, I’m all in favor of more people going armed. Just trying to point out that there will inevitably be costs associated with doing so. Wise men count the likely costs of a policy before implementing it, they don’t pretend there will be no cost.