What a can of worms! Drone killings are one of those, "it seemed like such a good idea at the time", stuff that comes back to haunt the people that dream them up.... like getting the Saudis to finance the war against the USSR in Afghanistan, for example.
Another downside is that the technology involved isn't rocket science.... radio controlled airplanes and helicopters are on sale even in toy stores in developed countries.
Stop and think how easy it would be to use a toy helicopter with an incendiary grenade attached to it over as "target rich" an environment as the Isle of Manhattan. Then just think how disruptive it would be for normal life there to even jam all the junk-band radio frequencies used to operate RC models (and so many other devices) in order to prevent such an attack.
For a country as potentially vulnerable as the USA to use this technology as a primary weapon system is like telling children not to put beans up their noses: it is putting ideas in the heads of people without much technology or money to spend.
It is really time for a wide ranging discussion about how we got here and how to go in another direction, as difficult as that might be.