It's a fair point that humans don't magically make this go away, but the thrust of the argument above is that robots are likely worse, because they lack any cap

It's a fair point that humans don't magically make this go away, but the thrust of the argument above is that robots are likely worse, because they lack any capacity at all for questioning or for remorse, and they also allow great physical detachment from the horrors they can cause. They don't stop to eat or sleep either, and they'll certainly do things that can cause their own destruction. Humans also may be even likelier to be loyal than moral if a drone with a gun follows them around to keep them on-side.