It never was proliferation of nuclear weapons we had to worry about, because the things are just too damn difficult to build. The weapons that transform the world are the ones simple enough to copy in a low-tech undeveloped environment.

Like the AK-47. It's been estimated that the design is responsible for more deaths in the 20th century than any other weapon ever known. Hitler and Stalin and Pol Pot et al murdered fewer people than AK-47s. That cheap simple little rifle is the worst weapon of mass destruction ever invented.

Until perhaps it's surpassed by killer drones you can build from an RC kit and a cell phone. Or--best remember when we are--printed out by an open-source "3D printer" using public domain plans found on the Internet.

Same as it ever was, but worse. Always worse.