The rationale then will be that if we can send a robot instead of a human into war, we are morally obliged to do so, because it will save lives — at least, our soldiers’ lives, and in the short term. And it is likely that robots will be better at applying the most straightforward laws of war than humans have proven to be. You wouldn’t have the My Lai massacre of the Vietnam War if robots could enforce basic rules, such as “don’t shoot women and children.”

And then there will be questions of chain of command. Who is accountable in the event that something goes wrong? If a weapons system has a design or manufacturing issue, the manufacturer can be held accountable. If a system was deployed when it should not have been deployed, all commanders going up the chain are responsible. Ascribing responsibility will still be a challenging task, as it is with conventional weapons, but the more important question is: Should the decision to take a human life be made by a machine?

Lethal autonomous weapons systems would violate human dignity. The decision to take a human life is a moral one, and a machine can only mimic moral decisions, not actually consider the implications of its actions. We can program it, or show it examples, to derive a formula to approximate these decisions, but that is different from making them for itself. This decision goes beyond enforcing the written laws of war, but even that requires using judgment and considering innumerable subtleties.