Talking Points Memo has an illuminating clip on the perspective that let the US get to this point.
Pay special attention to the section from about 0:48.
Note that the Bush apologist makes much of the US government "doing everything possible to keep us safe."
The problem here is what is possible.
Waterboarding is possible. So are sleep deprivation, stress positions, sensory deprivation and a host of other documented practices employed by US intelligence and advocated and approved by the Bush Administration. They are demonstrably possible: their use is documented.
So too, however, are the use of thumbscrews, the Brazen Bull, the Iron Maiden, the rack, drawing and quartering, and a host of other methods and devices known to history. I doubt strongly that anyone would advocate reintroduction of those methods of coercion. Yet, as the tools exist, and have both a long and bloody record and precise documentation of their construction and application, the possibility of their use is demonstrable and the possibility that they could be used today is very real. Possible only means that the capacity for use is measurable; it has nothing to do with the propriety of that possibility.
The problem isn't what's possible. The problem is what's ethical and legal. Were the question only one of the possible, all manner of atrocities could be justified. Civilisation is not about the possible, nor even about the practical. It is a matter of the ethical, moral, and conscionable: without ethics and some semblance of morality civilisation is impossible.
None of the techniques described fit those constraints.
H/T Andrew Sullivan.