It's not that they are too lethal. It's "we will not build a weapon system that is fully autonomous and acts without a human in the loop".

The big boy defense contractors won't touch that shit either because as soon as you mention the idea the engineers start shouting you down from the top of their lungs out of shear unbridled terror and the lawyers come storming in due to the endless legal risk said design would bring.

Mass Domestic surveillance sure they might do no problem but fully autonomous killbots or drones are gonna be a no go from pretty much every contractor other that doesn't carry a "missing the point of Lord of the Rings" name