How would you accomplish this without a firearm? Do you think you could accomplish this with a bat or a knife? The attack happened at a Walmart. They sell hard objects. This couldn't have gotten far. I can't imagine a location or situation where you could be so effective in harming so many without a weapon that gives you so much distance from your victim.
Do you have kids? I have one. Every day I look at my toddler and have to think about how to keep her safe (statistics are in my favor but they were in every parents' favor). Then I have to look at my wife and assure her that our baby will be able to live a long life.
I'll relinquish my second amendment rights, if I never again ahave to live through a year where there are more mass shootings than days. For now, we're just moving out of Texas.