When it comes to coercive interrogation techniques like water boarding, regardless of whether it is torture or not, there is a legitimate discussion to be had about whether it is justified in a ticking bomb scenario. It is unpleasant but not seriously harmful so whether that outweighs the potential mass slaughter that may be prevented* by water boarding someone like Khalid Sheikh Mohammed is a dilemma. I am genuinely ambivalent about what has happened to him, I don't like the idea of subjecting prisoners to water boarding but I don't like the idea of letting hundreds of people be killed by the terrorist cells that he gave up.
That said most of the uses of 'enhanced interrogation techniques' were not for the purpose of preventing imminent attacks and saving lives, but instead used to confirm the Bush administration's preconceived notions of Iraqi - Al Qaeda links, which is both a retarded way to interrogate anyone and renders arguments over whether that the ends can justify the means rather moot, as there were no credible ends in the first place.
As I've said before I don't think prosecuting anyone makes much sense from a legal or pragmatic position, but the treatment of those prisoners really was shockingly incompetent and served no discernible purpose and those that thought it was a good idea should have to explain themselves to the public in full.
* I discount the idea that "torture doesn't work", as merely a slogan to avoid having to decide between two hideous alternatives. Torture can work, just today for example is an news story about a criminal torturing a hostage in order to get her bank details and various examples can be found throughout history.