If the majority of the men in the shopping center in El Paso were armed, would it have reduced the damage done there? In the Old West, the murder rate was actually considerably lower than it is now nationwide. We should make firearm training mandatory for all men 18 and older.
No.
Why?
Because most people are not living in the fantasy land the right wing believe exists via watching way too much television and listening to far too much NRA propaganda
The Clackamas Town Center shooting
Two people were killed and a third was seriously wounded in Clackamas County, Oregon, when Jacob Roberts opened fire in a local shopping mall. Nick Meli, a shopper in the mall, drew a personally owned firearm on Roberts, who then retreated. Meli did not fire his weapon, for fear of striking bystanders.
The Golden Market shooting
The details are murky but according to reports, a man entered a Golden Market in Virginia in 2009 and began firing a gun. He shot and wounded the clerk and then began firing at patrons inside. He ran out of ammo and was attempting to reload when he was shot, wounded, and then subdued by a permit holder who happened to be in the store.
The New Life Church shooting
A former police officer from Minnesota named Jeanne Assam was at church when a 24-year-old gunman named Matthew Murray began firing at parishioners in the parking lot. Murray claimed two victims before Assam opened fire on him with her personally owned concealed weapon. After receiving multiple hits from Assam, Murray then shot himself.
The Parker Middle School dance shooting
Andrew Wurst showed up to his middle school dance with his .25-caliber pistol. He fired it, killing a teacher, wounding a second one, and injuring two students. The 14-year-old's shoot-out lasted about 20 minutes. It was ended when James Strand, the owner of the banquet hall the dance was happening in, confronted Wurst with his personal shotgun. He ordered Wurst to drop his weapon and held the teenager in place for 11 minutes before finally getting him to drop the weapon and lie on the ground, and then searched him for other weapons.
(I personally don't like the idea of stopping a shooter with a shotgun in a confined space, like a dance floor.... but it makes the case)
The Pearl High School shooting
Luke Woodham fatally stabbed and bludgeoned his mother and went on to kill two students and injure seven others at his high school. Woodham was stopped by Assistant Principal Joel Myrick, a U.S. Army Reserve commander, who detained Woodham by using a .45 caliber semi-automatic pistol he kept in his truck, until authorities could show up.
And these of course are just examples of private armed citizens stopping mass shootings. It doesn't include the thousands of individual crimes stopped each year by armed citizens.
And I also skipped over off-duty police who stop crimes all the time.
You are the one living in a fantasy world.
Most of the time a shooter confronted by one single armed citizen, will back down. And like the Town Center shooting, just simply having a gun alone, is enough to make the shooter back down, without even firing a shot.