THE SHOOTING death of Trayvon Martin has shone a light on a new breed of law that enforcers accurately predicted would lead to the kind of confrontations that took the life of the Florida teenager.

Mr. Martin was killed in February by George Zimmerman, a neighborhood watch volunteer in his Sanford, Fla., townhouse community. Recordings of the 911 call made by Mr. Zimmerman to police show him stalking the 17-year-old, whom he described as suspicious and possibly high on drugs. Mr. Martin was unarmed when he was shot, but Mr. Zimmerman was not charged with any crime — in part because of Florida’s “Stand Your Ground” law.

Florida enacted the law in 2005, becoming the first of some 20 states to adopt such a measure. The law shields individuals from prosecution if police determine they used deadly force in self-defense. This much is relatively uncontroversial, given that individuals have always had a right to defend themselves against attack; these protections are particularly strong if one is attacked inside the home.

What makes the Stand Your Ground law dangerous is that it absolves the individual of any responsibility to consider other ways to avoid harm. Before Stand Your Ground laws, police and law enforcement officials assessed whether a “reasonable person” would have resorted to the level of violence used to thwart an attack; the new law turns that standard on its head and immunizes an individual from criminal charges if he asserts he had a “reasonable” fear of grave harm. Florida’s Stand Your Ground law applies wherever the person has a right to be — whether in his home, his car or his business or on a public sidewalk.

According to the Tampa Bay Times, Florida experienced an average of 34 “justifiable homicides” before 2005; two years after the Stand Your Ground law was enacted, the number jumped to more than 100. Similarly disturbing spikes have been found in other states with similar laws. According to an analysis of FBI data done by the office of New York Mayor Michael R. Bloomberg (I), who co-chairs the 650-strong Mayors Against Illegal Guns, states that passed Stand Your Ground laws experienced a 53.5 percent increase in “justifiable homicides” in the three years following enactment; states without such laws saw a 4.2 percent increase.

The Association of Prosecuting Attorneys opposed Stand Your Ground laws, arguing that they were unnecessary and likely a danger to public safety. In a 2007 report, they foreshadowed the Trayvon Martin tragedy. “Although the spirit of the law may be to allow the public to feel safer, the expansions may instead create a sense of fear from others, particularly strangers,” the report said, concluding that enactment would have a “disproportionately negative effect on minorities, persons from lower socio-economic status, and young adults/juveniles” who are often unjustly stereotyped as suspects.

These laws should be scrapped. So should legislation passed by the U.S. House and recently introduced in the Senate that would force states to allow nonresidents to carry concealed weapons if they are permitted to do so in their home states.