Jim Holt: “Defenders of the doctrine of double effect appeal to Kant's categorical imperative: A person is always to be treated as an end, never merely as a means. And treating people as a means—to send a message, to create wider panic, to demoralize the enemy nation they are a part of—is precisely what the perpetrator of an act of terror does.”

The article cites an book review (which I haven't yet read) by Michael Ignatieff, someone I've been coming across a lot lately.