For even though the law on armed conflicts defines the principle of proportionality as a good relation between estimated collateral damages and the scale of the military advantage expected, it provides no estimated scale nor, clearly, any unit of measurement. As Sharkey points out: “There is no known metric to objectively measure needless, superfluous, or disproportionate suffering. It requires human judgment. No clear objective means are given in any of the laws of war for how to calculate what is proportionate” (Sharkey, “Killing Made Easy”). To convert the principle of proportionality into a calculation would be like adding together apples and pears without any method of recognizing them. What is the commensurability between a particular number of lost civilian lives and an expected military advantage? What could the common unit of measurement be? However, as Eyal Weizman has shown, this kind of calculation, as necessary as it is impossible, serves solely to legitimate the deaths that result, and serves this function simply by being done.

Grégoire Chamayou, A Theory of the Drone, loc. 1128