Killer robots. Call me nuts, but then smart autonomous killing machines appear, which don't require human control (so zero empathy), then it will come, slowly.

Killer robots. Call me nuts, but then smart autonomous killing machines appear, which don't require human control (so zero empathy), then it will come, slowly. It's already hard to protest against anything with police in control, and when army steps in they can take complete control (see army coups in some other countries). Taking humans and their 'silly' empathy out of the equation would just make that even easier. Just don't cause too much unrest at once. And some countries already can't be stopped. See Russia, a mafia state. They just beated protests until 'morale improved'.