I don't believe that humans can be reduced to homo economicus, but as a group, government officials are remarkably sensitive to financial, political, and reputational costs. Thus, when new technologies appear to reduce the costs of using lethal force, their threshold for deciding to use lethal force correspondingly drops. If killing a suspected terrorist in Yemen or Somalia or Libya will endanger expensive manned aircraft, the lives of U.S. troops, and/or the lives of many innocent civilians, officials will reserve such killings for situations of extreme urgency and gravity (stopping another 9/11, getting Osama bin Laden). But if all that appears to be at risk is a an easily replaceable drone, officials will be tempted to use lethal force more and more casually.
Rosa Brooks, How Everything Became War and the Military Became Everything: Tales from the Pentagon
drone-attacks, war