Machines don't kill people....people kill people.
Those machines defend people.
Unfortunately, the cost-effectiveness of these machines' ability of killing / defending "people" is no longer as positive as it used to be.
F-35 for example. This killing machine is a great achievement of political-scientific-engineering-technical-....-correctness but a catastrophe of cost-effective control. How on earth a machine would kill / defend people even if people couldn't afford to buy it?