I'm surprised terrorists haven't thought of this yet.
Modern technology is scattering all sorts of lethal vulnerabilities into our society. Can you imagine the possibilities? Driver-less car bombs? Anti-aircraft drones patrolling airports and bringing down airliners? Ambulatory autonomous robot mines? Put one in a small motorboat or yacht and you have the ability to take out an aircraft carrier or nuclear submarine while its tied up at the dock.
Just because its possible to make something and just because it will be easy to sell it to somebody doesn't necessarily mean its a good idea.