Last weekend, gun rights activists marched at the Alamo in San Antonio, Texas, carrying semi-automatic rifles and loaded magazines. Four days later, eighth-grader Andy Lopez was shot to death by Santa Rosa, California police for failing to drop the BB gun he was carrying to a friend's house.

Men carrying AR-15s down the street, fine; boy carrying BB gun down the street, fatal? Something does not compute.

In fact, the tragic killing in the second case exposes the fraudulent politics of the first. Guns are deadly. And death is fearsome. That's why skittish police shot a 13-year-old boy in cold blood: They were afraid of being shot themselves. They were scared of a gun -- even a piddling one in a boy's hands.

There will be an inquiry in Santa Rosa, where citizens are angry over the death of a child. Police will have to answer for the officers' recklessness. In effect, the authorities will have to explain why the officers' professional law enforcement training was insufficient to overcome their natural fear of a gun.

Gun rights extremists understand that fear very well. Here is the New York Times report of the Alamo gun rally:

Rally organizers and participants said they wanted to remind San Antonio that the carrying of rifles was not only legal but normal, and that the carrying of unconcealed weapons in public was no cause for alarm. But at the request of organizers, most at the rally stuck plastic straws or strips into the chambers of their rifles to show that though there might be bullets in the clip, there were none in the chamber.

What the rally organizers implicitly acknowledged is that it is impossible to differentiate an armed ideologue from an armed sociopath on a public street. In order to assure the world that they were the former and not the latter, the organizers asked rallyers to show that they were socialized and sane. How? By placing straws in their weapons, making it obvious they understood that walking down an urban street with a rifle is inherently "cause for alarm" and, indeed, anything but "normal."

The open carry movement is based on a myth and a lie.

The myth is that the U.S. was a gunslinger's paradise until repressive 20th century cosmopolitan mores spread across the land, crushing freedom. Take a look at this 19th century photograph of Dodge City, Kansas -- yes, that Dodge -- and you'll get a sense of just how deeply American gun regulation is.

Tombstone, Arizona, setting for both Wyatt Earp's shootout and an excellent memoir by Justin St. Germain, also enforced gun control. Disarming men who violated the town's firearms restriction may have been a cause of Earp's shootout.

The lie is that gun rights ideologues want to carry guns openly in public just because it's so gosh-darned normal. The desire for open carry surely derives from more than one psychological strain. But one intention is clearly to intimidate others -- physically and politically. Guns scare people for good reason. And people with guns know that -- with or without straws.

(Francis Wilkinson is a member of the Bloomberg View editorial board. Follow him on Twitter.)