Neither side wants to look softer than the other on terrorists. Hence the bipartisan support for the strikes. Liberal groups that might be inclined to protest the policy have been quiet because Obama put it in place. The lack of debate about our reliance on drones is a shame, because there are both practical and moral objections to it. …

Another concern, raised by a few liberals, is that the strikes have increased anti-Americanism abroad. (On “Homeland,” one of them turns an American soldier into a terrorist.) The Pew Research Center has found strong opposition to drone strikes in almost every country. The strikes may also be setting a dangerous precedent, goes another argument, since “more than 70 countries now own some type of drone.”

But the morality of the policy is what most deserves scrutiny. The tradition of thinking about wartime ethics holds that it is permissible to cause the death of innocent civilians under certain conditions: when the war itself is just, the deaths are unintended and the number of innocents killed is proportional to the good the military action is expected to achieve. …

The alternatives to drone strikes have costs. Ground operations would also cause civilian casualties and could put American troops at risk. Scaling back the drone strikes risks letting some terrorists go to plot more evil. But the costs of killing, injuring, endangering and terrifying civilians have to be entered into the equation.