The possibility that someone might arm a drone, legality be damned, is more pressing than the Second Amendment implications, Brookings' Singer says.
"There's a risk of terrorist or criminal use of this technology," Singer says. "People are thinking about packing these with explosives and carrying out 9/11-style attacks."
In 2011, the FBI arrested a Massachusetts man named Rezwan Fedaus who planned to pack a remote controlled airplane with explosives and fly it into the Pentagon. In the Middle East, Hezbollah has used rudimentary armed drones against Israeli forces.
Ferdaus got caught because he tried to collaborate with FBI agents posing as al-Qaeda operatives. But using a remotely-piloted vehicle makes it inherently more difficult to catch a criminal or terrorist, says Tony Hallett, CEO of Community Research Corporation, a Pennsylvania-based consulting company that is exploring the forensic problems that drones will present. In an upcoming academic paper, he argues that home grown drone attacks are inevitable.
"Most street cops aren't ready for this—it's not going to occur to them that an attack that just happened might have happened because of a drone," he says. "Conceivably, you can put a gun on a drone and a guy can sit on the other side of the country with an iPad, fly it into a crowd and open fire, then fly it away and crash it into the river. Who's going to solve that? It'll leave no trace evidence at the scene, nothing."
For now, seriously-armed drones remain primarily a military asset, and few people have the $17 million necessary to buy a Predator drone. But as technology improves, as it always does, mounting a gun on a hobbyist drone will no longer be a technological hurdle – meaning Rand Paul's nightmare scenario wouldn't necessary be exclusively reserved for government agencies.
"Technology-wise, you could solve the recoil issues," Singer says, referring to the Texas police department's plan to use a non-recoiling shotgun with rubber bullets. "From there, the conversion from nonlethal to lethal rounds is a policy leap, not a technological one."