The public debate over civilian use of drones is intensifying. Variously called "unmanned aircraft systems", "unmanned aerial vehicles", "remotely piloted aircraft", or simply "drones", they are available for purchase by anyone for a few hundred to a few thousand dollars. They have strikingly useful capabilities. They can carry high-definition video cameras, infrared imaging equipment, sensors for aerial surveying and mapping. They can stream their video in real time. They have GPS, inertial guidance, magnetic compasses, altimeters, and sonic ground sensors that permit them to fly a...