For all of the talk about legitimate, non-murderous ways that drones may benefit humanity, these machines appeal to the darker side of human nature, too. Criminals will have all sorts of uses for drones.
International borders (and their accompanying border police) are pesky deterrents for drug smugglers. Drones offer potential for dropping drugs and other booty across border fences at a much lower risk. Not only are drones hard for the authorities to spot, but in the event that the drone is captured, the criminals will likely be miles from the scene.
In 2011, a wannabe terrorist named Rezwan Ferdaus plotted to bomb American targets by affixing explosives to a drone -- making it potentially lethal. But in a scenario that was criminal, but not a danger to human life, in a Brazil prison in 2012, authorities thwarted a drone helicopter loaded with cellphones intended for inmates.
And of course, it's not at all hard to imagine weirdoes from all over the place spying on people using drone-mounted cameras. In short, the potential for airborne mayhem is sky high.