"The barbarous custom of having men beaten who are suspected of having important secrets to reveal must be abolished. It has always been recognized that this way of interrogating men, by putting them to torture, produces nothing worthwhile. The poor wretches say anything that comes into their mind and what they think the interrogator wishes to know." —From a Napoleon Letter to Louis Alexandre Berthier in November 1798.
Torture can either be viewed as a punishment or as a way to gain life-saving intelligence. International conventions prohibit the former. Psychology studies suggest it's ineffective at the latter. Which brings us, once again, back to the question: Why do it?
Notes from the Senate Intelligence Committee report
Napoleon vs. Cheney: "Interrogation That Actually Works"; Icing on the "Hate-Cake". Posted 12/17/2014. Primary article reviewing this important subject.
Many of the interrogators' actions were shocking and cruel, but some might argue (and some have argued) that torture is a necessary tool for extracting information. This, too, is dubious. The Senate investigation revealed that the CIA learned most of the valuable intelligence it gathered during this period through other means.
Military leaders have known about the pointlessness of torture for centuries.