On a 100-degree day last summer, on Chicago’s southernmost edge, Willie Fleming, who goes by J. R. (“It stands for Just Righteousness”), crept up to an abandoned ranch house shrouded in overgrown weeds. The overwhelmingly poor and black neighborhood sits beside a 150-acre, 1,500-unit public-housing complex and is about as far — literally and figuratively — from the Loop as you can get and still be in Chicago. Nearly a quarter of the homes in the area had been empty for at least two years. Usually when J. R. scouts for properties to break into and take over, he looks for ones with unmown grass, a sign of vacancy and disregard. But this was excessive. “I don’t come back here without my air gun,” he said, backing away. A young couple next door had set up lawn chairs on the sidewalk. An infant in only a diaper tottered around them. “That’s the dead-dog cemetery,” the man announced, motioning to the ranch house.