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Some time back Atrios summarized the stupidity of the ticking time-bomb thesis by being, dare I say, "pragmatic"... IIRC, the point was you don't need to legislate for a ticking time-bomb scenario because no-one will ever prosecute a real-life Jack Bauer.
The problem with legislating for a ticking time-bomb scenario is that it directs intelligence officers to treat every situation as if there were a ticking time-bomb, and thus abuse every captive because their orders and training allow for this to occur.