I think Norman Geras is right:
An absolute prohibition against torture that is not grounded primarily in the inviolable individual right against being tortured must fail, I think. Rodin's focus on the doers won't work unless it starts from the done-to and what they suffer.This, in response to someone else's argument that torture degrades the torturer and their society and that this is a complete objection to torture.
There has also been another type of argument made against torture: reciprocity. If we don't torture their people, they won't torture ours. That doesn't hold so true in contemporary conflicts.
But as the arguments about waterboarding show, these objections aren't so controversial; it's the definition of torture that causes problems. To what extent is it permissible to subject a suspect, or even someone who has been convicted, to harsh treatment in order to extract information that might prevent another offence, and thereby save lives? And what sort of treatment is permissable and what constitutes torture and should therefore be prohibited. Specifically, is waterboarding torture?
Perhaps there's yet another way to look at this issue: the adversarial versus the legalistic ethic. The very fact that we have a legal system at all is in part to prevent an adversarial response to crime - and terrorism is a crime. An adversarial response involves the direct retaliation by a victim or their representative to a crime. This sort of response tends to be unbalanced. Sometimes, a victim isn't in a position to respond at all. Other times, they might over-react. The Biblical injunction to take an eye for an eye, contextualised, is an appeal for victims not to react to the theft of a sheep by killing the thief, his family, burning down his hut and ploughing salt into the ruins.
A legalistic response refuses to behave as an adversary, but rather subjects the accused to a series of procedures and sanctions that have been agreed in advance and that are designed to be proportional and fair. Most of all, they must be universal and always applied to everyone in the same position. This is not the case with waterboarding, which has been applied to a few people on an individual and arbitrary basis.
The idea that we can subject suspects to severe treatment in order to prevent new crime is adversarial rather than legalistic. While a rights based objection to torture, or indeed any harsh treatment that is applied to a particular person but not to others, is valid, it isn't necessary for an objection to waterboarding to be sustained. Waterboarding is in conflict with the rule of law itself, and that must be the principle objection to it.