> A civilian could easily buy a small fleet of drones, equip them with small IEDs or sarin gas, and fly them into otherwise secured areas with large crowds.
Easy? Is sarin gas freely available at big-box retailers?
Don't underestimate hackers. The internet is supercharging hobbyist hackers in many domains, including electronics, chemistry and bioengineering.
I doubt the precursors to nerve gases(the worst ones, anyway) are readily available, but they are probably a handful of undergrad-level reactions away from easily available chemicals.
Easy? Is sarin gas freely available at big-box retailers?