Nothing could have stopped the massacres this weekend, but we can bring down the casualty rates in the long-run. One way to do this might well be to focus on the rate of fire - the shooter in El Paso would not have been able to kill as many people with a handgun that he had to reload frequently. He could have brought in a few, theoretically, so it is no cure-all. But making shooters reload gives people a chance. No one needs a high-capacity magazine.
And having slower rounds - like come out of handguns - lowers the casualty rate too. We should look at controlling muzzle velocity of civilian weapons. No one needs to be able to fire rounds that tumble when they enter the body.
And you are much more likely to accidentally kill your family with your handgun than actually ever protect them in any real way.