And IMO if the KR used it, it's torture (although it probably was the least physically damaging routine in the KR torture repertoire).
Nonetheless, that doesn't mean that waterboarding should never be used. I think employing it against murderous psychopaths like Kahlid Sheik Mohammad and Ramzi Binalbish was an appropriate use of torture.
I think the problem is that there is a significant distinction between physically mutilating a person or doing them lasting harm (e.g., burning cigarettes, cutting, amputation, putting eyes out, rape, etc.) which we would never allow the military to submit a member of our own military to for training and causing someone pain or discomfort in a way that does no lasting harm (e.g., sleep deprivation, repeating songs over and over again, waterboarding, etc.) which we do subject some members of our own military to for training. In the sense that they are unpleasant and coercive, both are “torture”. In terms of morality and vileness, I think the first sort thing is a very different beast than the second sort of thing. And as for your point about murdering psychopaths, I think the humane treatment of prisoners should apply to enemies where we have some expectation of humane treatment for our own people if captured by the enemy as a reward. While I think we should err on the side of humanity, I don’t think would are obliged to show the same sort of restraint against opponents who brutalize and do unspeakable things to their captives, even when they are innocent civilians