Missouri gun proponents built on the repeal to legalize “permitless carry” by anyone 19 years of age or older, nullify l ocal gun-control ordinances, expand “stand your ground” protections and empower citizens to carry weapons into restaurants, bars, streets, schools and seemingly everyplace else. The police even lost the ability to disarm anyone carrying a firearm unless the individual was under arrest. The inability of local government to make gun laws threatened to turn Missouri into the “Wild West,” in the words of an exasperated City Council member in Webster Groves.

In Tennessee, N.R.A.-supported politicians pushed through legislation allowing guns in parks. Only after passage did people discover that the law weakened the state’s ability to restrict weapons at concerts and state fairs. A 2017 law in Arkansas permitted guns on college campuses — which made guns legal at Southeast Conference football games and other large sporting events. So-called guns-in-trunks laws in Ohio and some other states allowed employees to store guns and ammunition in their vehicles while at work — followed by jumps in the number of guns stolen out of cars. Sweeping open-carry legislation in Texas meant public libraries could not keep guns out of the stacks.

While these changes expand gun rights for certain people, they invariably lead to significant increases in injuries and deaths. Right-to-carry laws correlate with increases in violent crime and rising homicide and suicide rates, and also raise the likelihood that incidents of conflict like road rage or domestic arguments will turn fatal. For instance, homicides committed with guns in Missouri increased by 25 percent in the three years after the 2007 repeal, and more Missouri guns were recovered in crimes in neighboring states. Gun suicides rose over this period as well. Data from the Centers for Disease Control and Prevention shows that states with the weakest gun laws and highest rates of gun ownership invariably have the highest rates of overall gun mortality. A recent study found that they also have higher rates of mass shootings.

Beyond the direct health effects, allowing guns in public spaces changes how we interact with one another. My research shows that people become more wary when they think a stranger might be armed — a mistrust that fuels further gun sales. Racial tensions and stereotypes often accompany this anxiety. “I see white guys walking around Sam’s Club with guns on their hips,” an African-American man in Missouri told me, which he saw as armed racial intimidation.

In an ideal world, New York City might serve as a model for effective gun policy. Gun-related injuries and deaths have been falling for the past decade — not coincidentally, over the same period that the city got serious about gun laws. New York has remarkably low rates of gun trauma for a United States city of its size. Municipal and state laws and regulations also effectively limit gun trafficking.