The horrific killings in Charleston, S.C., once again raise the question of whether we would be better off with more armed citizens or dramatically fewer. This debate largely has been forgotten by Congress, but the battle rages on in the courts as the National Rifle Association challenges any effort at gun control, including prudent measures such as San Francisco’s safe gun-storage law and California’s efforts to restrict gun-carrying to those who have a particular need and are most likely to be responsible. Resolution to this debate will depend on whether data and concern for public welfare — or mythical visions of gun effectiveness — triumph.

It would be a lovely world if every time a bad guy came to do harm, a gun magically appeared in the hand of a potential victim. Indeed, an NRA board member seemed to have this idea in mind when he blamed the deceased minister of the Emanuel AME Church for his vote as a state senator against allowing concealed weapons in churches: “He voted against concealed-carry. Eight of his church members who might be alive if he had expressly allowed members to carry handguns in church are dead.” The statement is nonsense.

First, it was up to the minister to decide whether his parishioners could carry guns in his church, so the law was simply irrelevant.

Second, even if the law and the minister allowed guns in church, it is not clear whether the congregants gathered for a Wednesday night Bible study, including elderly and female worshipers, would have wanted to carry guns or would have been able to use them effectively if they did.

Contrary to the NRA view of gun-carrying, what is striking in the data about defensive gun use is how statistically unlikely it is that civilian gun owners are able to do anything about mass shootings or violent crime in general. A five-year study of violent crime in the United States found that victims failed to defend or to threaten the criminal with a gun 99.2 percent of the time — this in a country with 300 million guns in civilian hands.

More guns and more guns in the hands of law-abiding citizens could yield more instances of effective gun defense, but that benefit comes at a price: More guns inevitably puts more weapons in the hands of criminals.

Doubling the number of guns carried or stored in houses would mean that our country’s 4 million auto thefts and home burglaries each year would yield an even bigger payoff for criminals. The annual number of lost or stolen guns is already measured in the hundreds of thousands — higher than the number of cases in which a gun is used to thwart crime.

For this reason, San Francisco’s safe storage law is a prudent measure designed to prevent gun thefts and reduce the number of children who are injured or killed when they stumble onto unlocked guns in the home. Yet the NRA argues that the Second Amendment prohibits safe-storage requirements.

On June 8, the U.S. Supreme Court recognized such an argument as bogus and thankfully refused to further entertain the NRA’s legal challenge to the San Francisco safe-storage law. Yet Justices Clarence Thomas and Antonin Scalia, in dissent, were outraged that a city could impose such an interference on the ability to immediately fire a gun.

I doubt the judges understand that while about 80 individuals are killed during home invasions each year, the number of accidental gun deaths is roughly 1,000 and thousands of avoidable suicides result from our huge stock of relatively uncontrolled guns.

Earlier last month, an NRA lawyer argued to the Ninth U.S. Circuit Court of Appeals that California’s restrictions on gun carrying are unconstitutional, stating, “There is no evidence that crime went up where concealed carry is legal.” But a new study by my Stanford team of researchers shows that the states adopting right-to-carry laws on average had violent crime rates that were from 4 to 18 percent higher than if they had not allowed such gun carrying.

It doesn’t make sense to encourage more gun carrying for self-defense if this leads to more violent crime. Ninety percent of Americans want universal background checks for the nation and other sensible gun-control measures. Safety and democratic values will be promoted when the people demand that such action be taken. We can’t stop all the mass killings or homicides, but sensible gun control can help.

For more information about a recent study Professor Donohue led at Stanford that found that right-to-carry gun laws are linked to an increase in violent crime, go to http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2443681.

This article ran first in the San Francisco Chronicle on Sunday, July 5, 2015.