Obama and the Nuremberg defense

Obama has released memos detailing the interrogation techniques allowed to the CIA under the Bush administration.

Those agents who tortured suspects without exceeding the limits of the guidelines, will not be prosecuted. To me, this is the thoroughly demolished Nuremberg defense.

How is this acceptable to anybody? This "the past is over and can now be forgotten" attitude fundamentally undermines justice, since it brings the expectation that any incoming President would pardon anyone who acted "within the guidelines" in place at the time. Whatever those guidelines happened to be.