I don't think many people dispute whether espionage in general is a practical moral good (or at least neutrality)... In the sense that we live in a world where foreign governments keep secrets that can be dangerous to the survival of other governments.

I mean, in an ideal world we wouldn't have spies... But we also wouldn't have police or military.

And people with security clearance shouldn't get to individually determine what is right by their own moral code.

that seems arbitrary and at odds with the modern considerations of superior orders

I don't see why it's arbitrary.

It's not at odds with the dismissal of the Nuremburg defense because it was a violation of the international law. I do have to admit that is sort of a cop out since international law at the time was more moral than real law.

Another huge distinction is that nobody was charged at Nuremburg for not exposing the crimes, they were charged with aiding them. If Snowden had a moral issue spying on people, he could quit.

Also at Nuremburg, we were just punishing the losers of a war.