It's not that hard to make the devices since most of the components can be purchased off the shelf. Guidance systems, once the most difficult aspect in weapon system design is as simple as ordering up a GPS unit. Stealth is practically forced on modern drone builders looking for larger payloads by reducing the weight of the airframe and power plant and therefore turning to composites. Traditionalists always opted for high explosive ordnance but the subway attack in Japan using nerve gas shows that just about anybody can make lethal neurotoxins and a few gallons of pure evil go a long way.
Drones can be launched from just about anywhere. They don't need airfields and runways since all they need is a space wide enough and long enough to get off the ground. Returning is not in the plan. There is no particular reason to launch the drone close to the target. A drone built along the lines of Rutan's Voyager which had a crew of two and fuel enough to go all the way around the world without refueling in 1986 would easily have a 1000 pound payload.
Enemies of the United States would have no shortage of kamikaze pilots without any need for fancy electronics. Enemies of the government of the United States would have little difficulty putting together unmanned versions. Consider that these drones may not be considered dangerous by the ruling class in Washington but that is because the skies over DC are patrolled by armed aircraft and there are active ground based defenses scattered around it. However, drones intercepted and shot down before reaching their intended target have a characteristic common with all aircraft; there's just enough time and fuel remaining to get to the scene of the crash/explosion/chemical release. Anybody in the projected flight path to the target is at risk whether from an unplanned crash or from the deliberate destruction of the drone by other means.
I thought about this as I read General McChrystal's remarks today about how much hatred there is in the rest of the world for the US by those who oppose drone strikes. The first time I saw a reference to this was in "The Moon Goddess and the Son" by Donald Kingsbury. In the book the drone was built and targeted by disaffected Soviet hating young terrorists from Afghanistan protesting the Soviet invasion of Afghanistan.
All of this makes the utter waste and stupidity of the TSA and HLS more painful to put up with. Consider that the same effects can be achieved more easily with a truck bomb.