Amy Davidson, in "Torture is Free" at The New Yorker:
"Maybe what is meant is that torture is illegal but you don’t actually get punished for it..."
Torture is the philosophical cousin of war. When you convince yourself in the pursuit of a given end, inflicting violence on human beings is an acceptable means, you have war and you have torture. When you believe that an enemy is so fundamentally not like you, and thus is not worthy dignity or rights, you have war and you have torture.
Why won't torturers ever be punished, even though torture is illegal? Why can they boldly confess and defend torture? Because, I think, the same impulse that convinced (and convinces) people that war is justified (or at the very least can be carried out in good faith) convinces people that torture can be justified (or at the very least not a crime worthy of punishment).