As the Christian Science Monitor noted, creation of such machines is quite risky, as artificial intelligence may run out of control any moment. However, in modern wars agility is above all, and human factor in operation of the killer robots may seriously impede decision-making.
Now there is controversy in the Pentagon on how much liberty should be given to the machines to take decisions. "We have to be very careful that we don't design [autonomous] systems in a way that we can create a situation where those systems actually absolve humans of the decision", General Selva noted. He also added that "The notion of a completely robotic system that can make a decision about whether or not to inflict harm on an adversary is here. It's not terribly refined, not terribly good. But it's here."
The Pentagon justifies its development with the statement that Russia and China allegedly also design 'fast-moving, fully-autonomous killing systems'. Thus, the US will make robots 'not to use them', but to know how they work and how to counter them.