A.L. lays it all out:
...even if we were starting from a blank slate and we could simply ignore the fact that techniques like waterboarding are proscribed by numerous laws and treaties, to make a policy case for the use of such techniques, you would have to do much more than establish that they occasionally have produced actionable intelligence. Among other things, you would have to prove that 1) such information could not have been extracted using other means, 2) that the misinformation produced by such methods doesn't overwhelm the accurate information to the point of rending the whole exercise pointless, 3) that the strategic costs of using such techniques (international outrage, increased radicalization of the Muslim world, increased danger to U.S. troops, etc.) don't outweigh the benefits, and 4) the value of the information produced is worth the tradeoff of never being able to use that information (or the fruits thereof) in court and severely jeopardizing any hope of ever convicting that individual in any constitutionally compliant legal proceeding.