HOW THE ZAMUDIO STORY COULD HAVE GONE…. In the wake of shooting tragedies, it’s fairly common for conservatives to call for more gun ownership — the idea being there would be less violence if more of the public were armed.

This argument has already been presented in Arizona, where there’s already a new measure pending to arm politicians and their aides. One state lawmaker said, “When everyone is carrying a firearm, nobody is going to be a victim.”

There’s ample evidence that reality isn’t that simple. Some of that evidence comes from Saturday.

William Saletan reports today on Joe Zamudio, one of the heroes from Saturday’s massacre. As you’ve likely heard, Zamudio was in a nearby store when he heard gunshots. He took his own gun, clicked off the safety, and advanced towards the gunman.

When he got to the scene, Zamudio saw a man holding a gun and shouted at him to drop his weapon. Indeed, Zamudio very nearly shot the man holding the gun.

The man Zamudio saw, however, wasn’t Jared Lee Loughner; it was the man who’d wrestled the gun away from Jared Lee Loughner.

This is a much more dangerous picture than has generally been reported. Zamudio had released his safety and was poised to fire when he saw what he thought was the killer still holding his weapon. Zamudio had a split second to decide whether to shoot. He was sufficiently convinced of the killer’s identity to shove the man into a wall. But Zamudio didn’t use his gun. That’s how close he came to killing an innocent man. He was, as he acknowledges, “very lucky.”

That’s what happens when you run with a firearm to a scene of bloody havoc. In the chaos and pressure of the moment, you can shoot the wrong person. Or, by drawing your weapon, you can become the wrong person — a hero mistaken for a second gunman by another would-be hero with a gun. Bang, you’re dead. Or worse, bang bang bang bang bang: a firefight among several armed, confused, and innocent people in a crowd. It happens even among trained soldiers. Among civilians, the risk is that much greater.

We’re enormously lucky that Zamudio, without formal training, made the right split-second decisions. We can’t count on that the next time some nut job starts shooting. I hope Arizona does train lawmakers and their aides in the proper use of firearms. I hope they remember this training if they bring guns to constituent meetings. But mostly, I hope they don’t bring them.

To be clear, the point here isn’t to take anything away from Zamudio, or to question his heroism. On the contrary, he showed great courage, and it’s likely he played a role in saving lives on Saturday. He deserves the plaudits he’s received.

The point, rather, is that the common assumption — more armed citizens means more public safety — is more complicated than some conservatives would like us to believe.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.