The only harm is in waiting for autonomous weapons to start killing. What if we could have banned chemical weapons before the first clouds rolled over soldiers, killing between 30,000 and 90,000 of them outright in WWI (estimates vary widely), and causing an unknown number of lethal cancers in others? And what if the public had known about nuclear weapons during their development in the 1940s? Cities like Hiroshima and Nagasaki might still have been targeted, and fire-bombed with conventional weapons. A-bomb apologists have argued that more Allied lives might have lost, if Japan hadn't been stunned in surrender by a horrifying new technology, capable of leveling entire cities with a single bomb. Still, is there any doubt that, when faced with the prospect of the global proliferation of radioactive doomsday weapons, the world would have at least considered banning their creation?