Abstract Semi-autonomous robotic weapons are already carving out a role for themselves in modern warfare. Recently, Ronald Arkin has argued that autonomous lethal robotic systems could be more ethical than humans on the battlefield, and that this marks a significant reason in favour of their development and use. Here I offer a critical response to the position advanced by Arkin. Although I am sympathetic to the spirit of the motivation behind Arkin's project and agree that if we decide to develop (...) and use these machines they ought to be programmed to behave ethically, there are several major problems with his view as it stands. At present, it is not clear whether such machines would be capable of behaving more ethically than humans. More importantly, to the extent that humans would remain in the context of war, human moral transgressions will continue, especially in the face of complicated ethical challenges accompanying automated warfare. Moreover, even if machines could be more ethical than humans in certain ways and in certain situations, this says nothing about whether warfare that contains these machines would itself be overall more ethical than warfare that does not include them as participants, or whether the inclusion of lethal robots is the best way to guard against human moral transgressions in war. (shrink)