Another school shooting today. A 13-year-old opened fire at a middle school in Roswell, New Mexico, critically wounding two.

As I write, details on the incident remain scarce. But here’s something we do know. After this shooting, as after so many horrors past, a great number of Americans will insist that the right response to gun violence is more guns in more places. They believe that their guns keep them safe.

One of those who believe that—at least until recently—was Curtis Reeves. The 71-year-old former Tampa police captain had founded the city’s SWAT team. Retired from the force, Reeves still carried a .38 caliber handgun. On Monday, he carried his gun with him to a movie theater in Wesley Chapel, Florida, an exurban community 26 miles north of Tampa. Reeves became annoyed by a man in the row directly ahead of him who texted before the show. Reeves complained first to the man, then to the theater manager. A confrontation erupted. Voices were raised. Popcorn was thrown. And suddenly: a man was dead.

The dead man was named Chad Oulson. You know his story. It was the big gun atrocity of the day for the 24 hours before the Roswell shooting. Gun atrocities occur so thick and fast that few of them gain public attention, and even fewer hold it for long. Yet the Oulson killing broke through, at least for a little while, because it seemed so unusually pointless and stupid. As the sheriff of Pasco County told reporters afterward: “To have a retired police officer—I don’t know what he was thinking at the time. I can tell you, anybody, over a cellphone, to take their life, it’s ridiculous.”

Ridiculous doesn’t begin to capture it. Oulson was texting his three-year-old daughter. He and his wife were away from home together, and he’d kept their phones switched on so his child could reach him. Now that child is fatherless, and the wife is a widow. During the altercation, she placed her hand on her husband’s chest to restrain him. The same bullet that killed Chad Oulson struck and wounded Nicole Oulson’s hand.

Yet it’s possible the situation did not seem remotely ridiculous to the shooter. If witness reports are accurate, Oulson was the first to raise his voice. Oulson was a tall man, well built, and thirty years younger than Reeves. Reeves may well have felt threatened. And isn’t that the very point and purpose of a gun? To be drawn when its owner feels threatened? “Better to be judged by twelve than carried by six.”

Seated beside Oulson in the theater was Charles Cummings, a Vietnam War Marine combat veteran. Oulson’s body slumped onto Cummings. It was Cummings’ 16-year-old son, Alex, who called 911. “I can’t believe people would bring a pistol, a gun, to a movie,” Cummings said after it was all over. But of course people do bring pistols to the movies! In the wake of the slaughter in the Aurora movie theater, how often did we hear it said that people should bring guns to movies?

“Gun-free zones are a magnet for those who want to kill many people quickly,” wrote noted gun advocate John Lott after the Aurora shooting. “[O]ut of all the movie theaters within 20 minutes of [the killer’s] apartment showing the new Batman movie that night, [Aurora] was the only one where guns were banned.” Had the theater permitted guns, Lott continued, Holmes might have been stopped. “With over 4 percent of the adult population in Colorado having concealed handgun permits, a couple hundred adults in Cinemark’s movie theater #9 means that there is an extremely high probability that at least one adult would have a permit.”

There was at least one adult who carried a gun in the theater in which Oulson was shot to death. Perhaps Reeves imagined that he might use his weapon to prevent some terrible crime. Instead, he committed one.

One statistic often tossed about in the gun debate is the claim that guns are used for self-defense some 2.5 million times a year, once every 13 seconds. That statistic is based on a set of surveys conducted before 1995 in which gun owners were asked whether they could remember using a gun to meet any kind of threat over periods that varied from one year to as many as five years. The phrasing of the questions could include anything from confronting an armed intruder to picking up a shotgun before investigating a squawk in the chicken coop. This kind of hazy self-reporting, conducted almost a generation ago, is not likely to generate any kind of reliable information.

But there’s a deeper problem with arguments about “defensive gun use”—a problem forced home by the fatality in Wesley Chapel. When a gun owner self-reports that he or she brandished or used a weapon in self-defense, the gun owner stakes a claim that the person on the muzzle side of the gun was acting improperly and that the gun owner was acting appropriately and responsibly. Yet that is not always true. It is probably not even often true. Curtis Reeves was a man highly trained in the use of firearms: not just a police officer, but a police officer who had founded a tactical response unit. Yet the best-case interpretation of Reeves’ actions is that in a crisis, he panicked.

And the worst case? The worst case is that many people who carry guns for what they call self-defense are really engaged in intimidation and aggression. Here’s another Florida case:

Michael Dunn, a 45-year-old man, pulled into a Jacksonville gas station in November 2012. The next car over was occupied by four teenagers playing loud music. Dunn is white; the four young men, black. Dunn ordered the teens to turn down their music. They refused. An argument erupted. Dunn drew a gun and fired eight or nine shots at the teens, killing one of them. Dunn claimed that he had glimpsed a gun inside the teens’ car and therefore felt threatened.

It’s a good guess though that if Dunn had not been armed, the argument over the music would not have escalated to the point of violence—just as, if Reeves had left his gun at home, the argument over the texting would have subsided without incident. When gun advocates claim that guns protect people, they omit to say that guns protect people in situations that would not have been dangerous in the first place if the guns had been left at home.

That’s something to remember as Americans seek to understand—and try to find adequate responses to—this latest school shooting, and the many more that seem sadly certain to follow.