  Concerns over the risks associated with advances in Artificial Intelligence
have prompted calls for greater efforts toward robust and beneficial AI,
including machine ethics. Recently, roboticists have responded by initiating
the development of so-called ethical robots. These robots would, ideally,
evaluate the consequences of their actions and morally justify their choices.
This emerging field promises to develop extensively over the next years.
However, in this paper, we point out an inherent limitation of the emerging
field of ethical robots. We show that building ethical robots also necessarily
facilitates the construction of unethical robots. In three experiments, we show
that it is remarkably easy to modify an ethical robot so that it behaves
competitively, or even aggressively. The reason for this is that the specific
AI, required to make an ethical robot, can always be exploited to make
unethical robots. Hence, the development of ethical robots will not guarantee
the responsible deployment of AI. While advocating for ethical robots, we
conclude that preventing the misuse of robots is beyond the scope of
engineering, and requires instead governance frameworks underpinned by
legislation. Without this, the development of ethical robots will serve to
increase the risks of robotic malpractice instead of diminishing it.
