You gotta keep in mind what a non-state actor gets out of it, though. Contrary to popular belief, there aren't a lot of doomsday cults. Aum Shinrikyo? They just wanted to fuck shit up and that was totally their jam. But even ISIS wants to foment an apocalyptic war specifically in the Middle East... and that means US boots-on-ground. You do something super WMD-ful in the US and we begin by saturation bombing and then come through for cleanup once we've cratered the shit out of the theater. So even an outfit like ISIS, the most chaotic evil terrorist organization in memory, has to act in such a way as to provoke the US to do something rather than simply fucking up shit wherever they can.
Pulling down the grid doesn't benefit any non-state actor I can think of, outside of Hans Gruber, George Clooney/Brad Pitt or Enron (fuck those guys) and Enron did it within the system, no mayhem necessary. Do you have a scenario in mind?