The perpetrator has two significant advantages over the average person with a gun: He's first, and he's crazy. And if he sees the slightest hint that you're packing a gun, you're as good as dead. In reality, if he's close enough to want to take something from you, then he's close enough for you to use an alternative to a firearm. You'd be better off with one of these new high-tech 10 percent pepper gel devices made in Switzerland. I carry one myself and have never felt that a gun would make me any safer. At a deployment speed of 110 miles per hour (using airbag technology), and with an effective distance of 13 feet and a radius of about 2 feet, the gel can disable the perpetrator without killing him -- all before he figures out what that gizmo is in your hand. Besides, you're psychologically more likely to use it without hesitating, knowing that it won't kill the guy.
-- A gunman walks into a shopping center and opens fire with an assault weapon. In NRA-land, everyone would have a gun and just take the guy out. So if there were 100 people with guns present -- the NRA's dream -- every single bullet would slice through the bad guy and everyone would just continue on with their business. More realistically, everyone would be firing bullets into each other, into storefronts, into the guy dressed up in an animal costume handing out promotional flyers.
Indeed, there are people who have the skills, training, expertise, physical and mental rigor, discipline and psychological training to perform the sort of heroism that the NRA likes to attribute to anyone capable of holding a firearm. Those people are called snipers, and even among military members, they are uniquely qualified for their roles. Their specific psychological training to overcome the natural human aversion to killing at close range is what gave the British the advantage against the Argentineans in the Falklands War. People who believe themselves to be similarly capable probably also think that they can beat Michael Phelps in the pool.
We need sensible, effective, intelligent solutions, not gratuitously self-serving agenda-pushing. Because the more out of hand things get, the greater the risk of reaching the point of total crackdown on freedom.