It didn’t take long. Three days after a jury found George Zimmerman not guilty in the murder of Trayvon Martin, the Justice Department said it will take a “hard look” at a new type of self-defense law known as “stand your ground.”

Florida and nearly two dozen other states have passed such laws since 2005 in a campaign led by the National Rifle Association. The laws get rid of an old legal doctrine that anyone confronted by a dangerous person has a “duty to retreat” rather than shoot. And the laws provide greater legal leniency toward killers who claim they acted out of fear of harm or death.

That’s one reason Florida officials hesitated in arresting Mr. Zimmerman. He wasn’t charged for 44 days after the shooting. And even though his legal defense relied on a traditional self-defense argument rather than Florida’s Stand Your Ground law, the judge’s instructions to the jury specifically mentioned the law’s provision.

While it is doubtful a Justice Department probe can make a legal challenge against the state laws, the federal scrutiny is needed. Homicide rates have risen 7 to 9 percent in states with stand-your-ground laws compared with other states, according to a 2012 Texas A&M study. And findings by Georgia State University “raise serious doubts against the argument that Stand Your Ground laws make [the] public safer.”

The laws “senselessly expand the concept of self-defense,” Attorney General Eric Holder said Tuesday. They “try to fix something that was never broken” and have “victimized too many who are innocent.”

In addition to the Justice probe, the US Commission on Civil Rights began an investigation last May to see if stand-your-ground laws encourage racial killings. A study published by the Urban Institute found more homicides were likely to be deemed justified in states with stand-your-ground laws than in other states, while shootings of blacks by whites “were likely to go unpunished.”

But the main reason to challenge these laws is that they reverse the course of history. The rise of civilization has relied in large part on humans handing over the control and use of violence for protection and defense to the government. Societies built on moral codes that tell individuals “thou shall not kill” have proved to be more long-lasting. At a deeper level, they reflect an expanding respect for life, not just for family or nation, but for all.

Stand-your-ground laws give too much authority back to individuals to decide the places or circumstances in which they can use violence. Many people have only a vague understanding of the laws’ legal distinctions or are able to assess the probability of harm being done to them. Other people may purposely kill off a harmless opponent, claiming a threat was imminent and with little risk of being charged.

“When you make it easier for people to use deadly force, you get more of it,” said Mark Hoekstra, an associate professor of economics at Texas A&M University and the lead author of the 2012 study, which found these laws cause an additional 500 to 700 homicides each year.

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The popularity of the laws reflects growing distrust or lack of faith in government. “Lynchings, riots, civil disobedience and vigilantism are all expressions of individual or collective action that reject both legal norms and the authority of state actors,” writes Columbia University law professor Jeffrey Fagan. If that is the case, then America’s political system needs urgent repair.

Laws that make it easier to shoot first and ask questions later are not a hallmark of human progress. At a practical level, they seem to increase homicides, not stem them. For that reason alone, states with the laws have a duty to retreat.