Former CIA operative and current thriller writer Barry Eisler as interviewed by Scott Horton:
[T]orture is also an excellent way to get the subject to confess to anything at all, which is why it was a wonderful tool for the Spanish Inquisition and for the secret police of assorted totalitarian regimes. But if the goal is to produce accurate, actionable intelligence, torture is madness, as Alexander argues in his book, How to Break a Terrorist: The U.S. Interrogators Who Used Brains, Not Brutality, to Take Down the Deadliest Man in Iraq. To paraphrase Oscar Wilde, torture is worse than immoral: it’s tactically stupid. It produces false confessions, which can be used to confirm mistaken suspicions and even outright policy fantasies; it instills an insatiable thirst for vengeance in most people who are subjected to it, and so creates new, dedicated enemies; it permanently brutalizes its practitioners; and it cuts us off from intelligence from the local populace because so many people will refuse to inform on someone if they fear he’ll be tortured. [my emphasis]
Bush’s use of torture in the War on Terror demonstrated this amply – for example in the contrasting stories of Abu Jandal and Ibn al-Shaykh al-Libi.