It's only a matter of time before criminals/terrorists start arming drones and using them to commit crimes etc. People are also going to start flying them into aeroplanes and stuff which is a scary thought and a few have already had near-misses.
Well, those machines may have the weapons, but are still lacking the most important part: the strong (hostile) artificial intelligence behind their actions.
Why would they need a robot behind them when people can just control them manually.