Why do they torture? Well, ask why did they torture before?
From the Salem Witch Trials and burning women at the stake, to the Spanish Inquisition and their waterboarding invention, to modern day, torture is designed to produce political fiction.
When something comes straight from the horse's mouth, what comes back out, might be what what went into his mouth in the first place.
Useful political fiction is the torturer's primary reason for torture, number one, primary, not secondary. It has always been this way. It does not matter who is doing the torture. There is no good torturer.
The torturer has means, motivation, and opportunity to coerce his victim to vomit back the same political fiction which the torturer fed to the victim. It's no wonder torture is illegal. Put that in your pipe and smoke it.
Why do they torture? Well, ask why did they torture before?
"They" are torturers throughout history, low people, choosing the low road, very low. The process of torture outputs useful political fiction. That's the answer, if you look at history and the question, of torture.
Political fiction is not just a "possible risk" of torture. It's not that the torturer "might" receive lies from a tortured person. Torture is designed to produce political fiction. Torture is a Machiavellian fiction feeding tube.
The process of torture also inputs useful political fiction. That's part of the reason torturers prefer secrecy, as they don't want you to see that they are feeding and leading the "witness", as of course it would weaken their hold on your trust. When the occasional truth does emerge from torture, that is just a by product, a nice to have.
Water-boarding was invented by the Spanish Inquisition. The Spanish water-boarding indeed produced the precisely the type of desired religious confessions, from precisely the preferred choices of torture subjects, in order to produce fiction of the highest possible political value to the interrogators. It was no "coincidence" that the fictional accounts spouted by the tortured, just "happened to be" spot-on for the captor's desired subject of discussion, then, as now. The Inquisitors did not create water-boarding to elicit any factual information.
Political fiction was and is the intended result of water-boarding. Look back throughout history at the patterns of torture. Notice that the public at large are encouraged and expected by the torturing authorities, to trust that when "information" comes straight from the horse's mouth, the "information" would generally be expected to be true. The torturer intends that coercing the tortured to speak the torturer's political information, should help paint the color of truth onto the torturer's own statement.
Furthermore, the torturer could not really be held responsible by a sane person, if the captive lied to the captor, could he? It's"from the horse's mouth" after all, so we the public or third parties, can't really blame the interrogator for doing his best to get the "information" straight from "the source." If the torturer then acts on this "information" which came from the horse's mouth, any unfortunate outcome of acting on this information, is not centrally the torturer's fault is it? You would be a partisan, a hater, if you try to put that weight on the torturer, wouldn't you?
We are led by believe that should forgive the torturer, for acting in "good faith," if anything he acted on is found later to be fiction, on the off-chance that its falseness is actually discovered by the public. All these kinds of "outs" are for the one actually doing the torture, key to why they choose to use torture.
The Salem Witch trials in the colonial America resulted in many women being burned by fire often fatally by their government interrogators. Women actually were driven by fire to confess to being witches, per the "suggestion" of their torturers. Land-grabs by political insiders was eventually discovered to be the actual motivation for the "witch" torture in Salem.
Torture throughout history has proven time and time again, to be a politically "authorized" Machiavellian feeding tube, used by bad political actors, to transfer their most useful fiction of the day, into the mouths of the most useful surrogate mouthpieces to be found.
It is no surprise that here and now, water-boarding is the torture technique of choice. Of all the torture techniques, water-boarding is the favorite in modern America, for practical reasons.
Water-boarding leaves no marks on the skin nor internally, which is important to help save the skin of the torturer himself, as the torturer still has a degree of fear of getting caught by the evidence, by a society that still mostly outlaws torture, by a society that still mostly has an evidence-based concept of justice. It's a valuable precaution.
Just as important, those who would torture, will choose water-boarding for the advantage being that the torturer can reapply water-boarding as often as desired, such as daily, say until the desired political fiction is vomited, all of it, because zero body parts are worn out or eliminated with each iteration of water-boarding. Water-boarding ruins no organs during the victim's descent to death, until he reaches death. Yes at death there might be a problem, I'm no forensic physician, but to run from the science of forensics, the torturer would have to "disappear" the body. Better yet, the torturer would prefer to claim that it never had the person in their jail in the first place, such as by using a "black site" prison. If those become impossible, the torturer can resort to generating plausible deniability and point fingers, if it is known they had possession of the person, by passing the body to a foreign country, which might be another use for "extraordinary rendition.". Yea I bet you thought that "extraordinary rendition" could only be useful for live captives.
The Bush administration's Justice Department's secret memo on the new definition of torture -- the same definition which Attorney General Mukasey studiously avoided communicating to the Senate -- advised that organ failure was the new litmus test of torture. What a coincidence! Political fiction is not as useful, nor as popular, for a torturer, until it comes from a horse's mouth.