If they're too dangerous to fly over public roads all the time it's problematic to put them over people and houses on private property instead. (Leaving aside noise issues.) I imagine drones will have their place to do urgent deliveries especially where there aren't roads. But they suffer from the same problem that other heavier than air craft do (e.g. flying cars), their failure mode is falling out of sky on top of things--even with safety systems like parachutes.