They weren't really offered immunity, they were assured by the Office of Legal Counsel that they were doing something legal. Get bad advice from your lawyer as to what is legal and what isn't, go commit a crime, and see what happens.
"Shock and awe" == good
"Terror" == bad
"Torture" == illegal
"Stress position" == legal
decapitation with a knife == horrific and evil
decapitation by shrapnel == worthy of a medal
assassination by the American govt == good
assassination by other governments == bad
killing by poison gas on the battlefield == bad
killing by poison injections in a prison == goodIn what jurisdiction? duress (or necessity in general) is only rarely a valid defence in English law.
http://www.cnn.com/2014/07/23/justice/nazi-charge-philadelph...
On a side note, it was not exactly repealed, because you can't repeal an amnesty (ie voting a new law that removes it). They found that its creation was unconstitutional, meaning that it was void from the onset, like it had never happened. Learning about those 2 laws (+ley de pounto final for the ones giving the orders) when I was in Argentina was extremely formative on a law doctrine point of view.
I should start out by saying that I hope the torturers, their superiors, and enablers are prosecuted by anyone that can get their hands on them: a future US administration, the ICC, a European nation, anyone.
That said the US legal analysis is very tough. The lawyers they were given "bad" advice by weren't just lawyer, they were representatives of the sovereign that would seek to prosecute them. That raises due process concerns that aren't present in an ordinary advice-of-counsel defense.
In addition to Constitutional problems, the Detainee Treatment Act of 2005 and Military Commissions Act of 2006 create statutory defenses for torturers. The key language is "it shall be a defense that such officer, employee, member of the Armed Forces, or other agent did not know that the practices were unlawful and a person of ordinary sense and understanding would not know the practices were unlawful. Good faith reliance on advice of counsel should be an important factor, among others, to consider in assessing whether a person of ordinary sense and understanding would have known the practices to be unlawful." To be sure, that's not a unlimited immunity provision, but it does make prosecution more difficult. The Military Commissions Act also changed the substantive provisions 18 U.S. Code § 2441 (war crimes) to make much less conduct qualify.
Finally, except in cases where torture resulted in death, there are statute of limitation problems. Depending on which statute is use the limitation period for non-fatal torture or war crimes generally are either five or eight years.
In sum, there are many barriers to US prosecution. It may be much more practical for the wrongdoers to be prosecuted under the international law regime that began at Nuremberg. Given universal jurisdiction for violations of jus cogens this can happen in any country in the world, and there is no statute of limitations doctrine internationally.
As a practical matter I don't currently see the political will for prosecutions. If the public demanded it, maybe, but frankly I think a lot of the public feels complicit, in many cases unapologetically so. That all makes me very sad and I do hope these people start slipping up and travelling overseas...