Like other young women she knew who lived on the South Side of Chicago, Marimar Martinez carried a handgun at the bottom of her purse. The gun, a Smith & Wesson pistol for which she had a concealed-carry license, was usually strapped into a neon-pink harness. “It’s a girl gun,” she told me recently. Martinez is thirty-one and works as a teaching assistant at a Montessori school. She thought of herself as a trusting person who’d help “literally anybody,” even strangers.