The use of drones in military operations has steadily grown — we know from public documents that from last September to this March alone, C.I.A. operatives launched more than three dozen strikes.

The appeal of drone attacks for policy makers is clear. For one thing, their effects are measurable. Military commanders and intelligence officials point out that drone attacks have disrupted terrorist networks in Pakistan, killing key leaders and hampering operations. Drone attacks create a sense of insecurity among militants and constrain their interactions with suspected informers. And, because they kill remotely, drone strikes avoid American casualties.

But on balance, the costs outweigh these benefits for three reasons.