From the Brief Synopsis on the Army War College (U.S.). Strategic Studies Institute website: "While supporters claim that drone warfare is not only legal but ethical and wise, others have suggested that drones are prohibited weapons under International Humanitarian Law (IHL) because they cause, or have the effect of causing, indiscriminate killings of civilians, such as those in the vicinity of a targeted person. The main legal justification made by the Barack Obama Administration for the use of armed drones is self-defense. However, there is ambiguity as to whether this argument can justify a number of recent attacks by the United States. In order to determine the legality of armed drone strikes, other factors such as sovereignty, proportionality, the legitimacy of individual targets, and the methods used for the selection of targets must also be considered. One justification for the ethical landscape is the reduced amount of collateral damage relative to other forms of strike. Real time eyes on target allow last-minute decisions and monitoring for unintended victims, and precise tracking of the target through multiple systems allows further refinements of proportionality. However, this is of little benefit if the definition of 'targets' is itself flawed and encompasses noncombatants and unconnected civilians. This monograph provides a number of specific recommendations intended to ensure that the benefits of drone warfare are weighed against medium- and long-term second order effects in order to measure whether targeted killings are serving their intended purpose of countering terrorism rather than encouraging and fueling it."
Army War College (U.S.). Strategic Studies Institute: http://www.strategicstudiesinstitute.army.mil/