For a counterpoint, you might want to look into Argentina's "Law of due obedience"[1]. Of course, Argentinean law doesn't affect US law, but the fact that this law was eventually repealed sets an international precedent that "I was just following orders" is not a valid defense from prosecution.
"I was just following orders" has already been established as an insufficient defense in the 1946 Nuremberg trials and essentially all later trials against WW 2 war criminals. It is by now pretty well established that crimes against humanity in general and torture in particular are not justifiable.
This (along with striving to get good PR) is one of the main reasons the US government is so keen to redefine the word "torture" to mean something that they don't do. The same goes for the words "terrorism" and "terror".
"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 == good
What about when it is combined with duress? Like if you refused once and were told they would kill your family if you ever refused again or quit? I'm just curious. I agree with the spirit of the idea that following orders is not valid justification, but being under duress is a well-known and generally accepted justification for committing a crime. Can you shed any extra light on this?
War criminals who would have been shot for abandoning their posts (almost all of the low-level guys fall into that category) have been, and continue to be, prosecuted for those crimes. It's not a hypothetical, it's still in the news.
Yes, there is no amnesty for human right crimes, that means those people were only protected inside Argentina. And the Nuremberg defense doesn't work against the Nuremberg laws.
On a side note, it was not exactly repealed, because you can't repeal an amnesty (ie voting a new law that removes it).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.
[1] https://en.wikipedia.org/wiki/Ley_de_Obediencia_Debida