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.
My point is that in shooting incidents, law-abiding armed individuals have typically either chosen to keep their heads down or opted to put the assailant down. There's been no en masse multi-party fratricidal shootout involving dozens of casualties inflicted by law-abiding gun owners on each other that I've heard of. And this is over the course of over a century of near-universal gun ownership.