And so we come to the crux of the matter: which matters more, the possibility of gaining information that could keep US citizens safe, or the guarantee of violating the basic human rights of non-US citizens? Assuming that the captive you have in custody is in fact a terrorist withholding information that is detrimental to US citizens, subjugating them to water-boarding almost ensures that when they are captured by terrorists, these same methods will be used against them. At this point, morality leaves the equation, and you are left with a torture form that will most definitely be used against our own troops, which is something that both parties of government can agree is unacceptable.
Water-boarding is particularly torturous as it simulates the experience of death, something that most forms of torture can't replicate. Having your nails pulled out, being beaten, electrocuted, or humiliated are all painful and degrading, but at the end of the day, the victim knows that they are being tortured. With a form of torture such as water-boarding, the detainee doesn't know if at the end of the session, they are alive of dead. A similar example of mock execution is pulling the trigger of an empty gun on someone, thereby forcing them to imagine their death. These methods really put the "cruel and unusual" in punishment, and have no place in the future.