I'm not gonna get into this too deep. Just a couple of things.
First of all it would be nice, if we'd stop with the black and white. Some people in the NSDAP had their reasons for joining the party, some didn't. And not everyone in the Wehrmacht, Gestapo, SS etc. was a "Nazi". There were a lot of members of the Wehrmacht that were decidedly against the "Nazis". Stop with the uneducated, "inflationary" use of the word Nazi for everyone in the German military or everything German.
The name Mengele was tossed into the mix earlier. He is a prime example of a scientist and physician who had hardly any interest in the NSDAP and the SS. He joined both organizations, because they paid for his education and his later studies and they let him conduct his ethically very questionable and doubtful research. Without that we today probably wouldn't know who Josef Mengele was. Without his education, his work at the Kaiser-Wilhelm-Institut and in Oświęcim (Auschwitz), little Josef Mengele from Günzburg would probably never have become the "Angel of Death". Besides all that, he probably never was a real Nazi.
But there are some things one should consider. Joining the NSDAP meant joining a party that propagated genocide. Joining the SS meant joining a paramilitary organization, that carried out direct party and Führer orders behind the front lines as well as inside the whole territory occupied by the Third Reich, which meant hunting dissenters, fighting the guerrilla and the resistance, ethnic cleansing, genocide, deportation etc. So, even if it was an elite organization (which wasn't that elite at the end except from the Totenkopf division) and even if they paid for ones education etc., being in the SS meant being in an organization whose purpose often had little to do with the war itself. Most of the time, to the SS the war was just a smoke-screen that cloaked racial profiling, segregation, deportation, scorched earth and murder like clockwork.
I'm sure there are also a lot of al-Qaida members, who just wanted to help their families, stand up for their religion or country or anything like that and who never even took a shot at an American. Still, if you admit to being a member of al-Qaida, you probably go to prison in the US for a long time. Considering that, I'd probably prefer being a Nazi, because that means I probably wouldn't get tortured in a US prison or something like that.
That said, one can't judge someone (legally and morally) solely by his actions. One has to consider the circumstances under and the times in which the action took place. But there are still moral and ethic standards in a democracy. Arguing everything with the point "it was war" is not a fit argument for a democratic assessment and judgement of a taken action, even if it happened in the past. He killed and was member of an organization that specialized in killing, whether it was legally always murder or not is another point, it's in these cases often the intention that counts.
