When news broke of the latest mass shooting, someone where I work remarked, “Too bad there wasn’t someone with a gun there to stop it.” I said that he was assuming a good guy with a gun would be a better shot than a bad guy, to which he replied, “At least you could try to do something.”
It would be very easy to be the bad guy with a gun. The bad guy has the element of surprise. The bad guy has the advantage of planning. (They can even plant bombs!) The bad guy doesn’t even need to be a good shot. So what if they hit the wrong people? They probably aren’t making that distinction anyway. With enough firepower, accuracy is not a big concern to the bad guy.
On the other hand it would be very difficult to be the good guy with a gun. The good guy will be caught by surprise. The good guy has to react instantly to a deadly situation. And the good guy can’t miss. The good guy can only shoot bad guys. How many people outside of law enforcement have that kind of skill and training?
And the good guy would be putting himself squarely in the line of fire, not only from the bad guy, but from the police and even from other would-be good guys with guns. How do you tell the difference between a good guy and a bad guy if they both have guns?
So yes, if everyone had guns they could all “do something.” They could make things even worse.