Two articles on Truthout, here, and here, explain the true purpose of waterboarding and other forms of abusive interrogation: to obtain statements from prisoners supporting the political agendas of the captors.
All intelligence operatives know that information obtained by torture is unreliable. Prisoners will say anything to stop the abuse and pain of torture. Anything obtained through coercive interrogation techniques must be scrupulously verified externally and is therefore of little value.
The most successful results of torture have always been statements by prisoners supporting the agendas of their captors and opposing the their own participation in acts of war. In Korea and Vietnam, torture was used to coerce American soldiers and airmen into testifying against the United States and in support of the country the United States was invading.
What we've learned from the experience in Iraq is that the use of torture by the United States erodes the moral position of our presence in Iraq, refuting democracy rather than supporting it, and promotes the recruitment of individuals dedicated to ending the US invasion and occupation of their country.
Torture is not only evil and immoral, it is counterproductive to the espoused ideals of the United States. Torture, or anything that smacks of torture, has no place in US foreign or domestic policy.