I think the amount of people who like to collect guns & play war games, with basically all govt restrictions on weapons ownership removed, would probably serve as one of the greatest deterrants ever. Red necks are currently viewed as a serious threat to our govt despite being seriously crippled by regulations on what they are allowed to own & our govt basically being the most heavily armed govt in the history of the world.

I think drone tech & open source Ai tools & cryptography are really only going to make the economics better for individuals & defense vs larger institutions & offensive measures in the long run. 

 Exactly this. You would not try to overthrow a country where its citizenry is heavily armed, because they will defend themselves. Meanwhile, the US military does not even exist for defense, it is a purely offensive force. And a disarmed citizenry with a centralized power center is a relatively easy target - you just have to take out or subvert the leadership.