A Yemeni civil engineer recently recounted to US Congressmen how he witnessed a drone strike that took the lives of his brother-in-law and nephew.   His brother-in law was a cleric who had spoken out against Al Qaeda and was unfortunate enough to have been meeting with Al Qaeda militants when the drone struck them.  The Al Qaeda were reproaching him for his public statements.  His son had come along for protection.

Despite their vaunted surgical accuracy, drone strikes kill innocent civilians as well as presumed terrorists.  Estimates vary, but there is little doubt that hundreds of non-combatant bystanders have been killed by our drones during the course of the past decade.

The practical argument against drone strikes is that they are self-defeating: they generate resentment that breeds terrorists, very possibly creating more terrorists than are killed.   I find that argument compelling, but right now I want to focus narrowly on the morality of drone strikes.  How can they be justified, given the likelihood of incidental civilian deaths?

We kill people identified as terrorists because we believe that if allowed to live they will kill Americans (or others).  Let’s assume that we are accurate in identifying terrorists and that we assign zero value to their lives—they are bad people who want to kill us, so we can’t be squeamish about killing them.  We nevertheless have a moral obligation to worry about the innocent people who die when we kill the terrorists.   The deaths of innocents can only be justified on the assumption that the Americans eventually killed by our targeted terrorists would outnumber the innocent people killed by our drone strikes.  But we can’t really know for sure that our targeted terrorists will ever actually succeed in killing Americans; much less can we know how many Americans they will kill, or when they might accomplish that objective.

So, if we think drone strikes are morally justified we are saying that the speculative future deaths of a necessarily unknown number of Americans can justify the present deaths of an also unknown (except maybe after the fact) number of innocents.   I think that that is a very, very hard case to make.  Which is why I am very skeptical that drone strikes, except perhaps in highly exceptional circumstances, can be morally justified.