Methods A, B, C and D

What prevents these methods from being used with rifles? What is special about robots in this context?

Even if he's wrong do you deny that it's likely that technology will advance to the point where people can make robots capable of killing without a human making the decision?

No, we already have those. The decision to kill has nothing to do with it. The decisions of where to put the robot, and its ammunition, and the fuel, and everything else it needs, so that it's in a position to make the decision to kill, is what we cannot yet do programmatically. You're confusing tactics and strategy. You cannot run an army without strategic decisionmakers. Robots are not in a position to do that for, I would guess, at least twenty years.

Hitler. Milgram experiment. Number of sociopaths: 1 in 20. Is rationality taught in school?: No.

Ok, so this being so, how come we don't already have oppressive societies being run with plain old rifles?