Exactly.
The fact that there were people who willingly build and ran these camps clearly proves that morals are variable and not absolute. Or else there would never had been camps at the first place.
As for “the right to tell the german that they were bad” . The rights are precisely based on morals. The nazis thought the correct thing to do was to kill the Jews, hence that they had the right to build camps. Other people thought that was wrong, hence that they had the right to bomb the nazis. What you personnally think on this issue is irrelevant. People just don’t have the same morals. Were you born around 1920 in Germany, perhaps you would have applauded.
Once again, slavery have been accepted in most societies in the past. We’re more of an exception on this. You’re don’t belong to our tribe/country/race? You’ve no rights. You’re weaker than us? Too bad, we’re going to kill/enslave you. That’s the way it worked for most of human history, and people, on the overall, had no much of a moral issue with this. And in these societies, there were thinkers, moralists, priests, philosophers, etc…But most of them just didn’t get there was something problematic with slavery. Were they all stupid, unable to see the obvious? Or is it that they had a different set of basic assumptions and thought and worked on these assumptions, considering them self-evident, in the same way we consider self-evident that slavery is bad?
Taking again this example. PETA and similar organizations are currently telling us that killing animals is evil. There are more and more people who become vegetarians for moral reasons. A lot of people dislike killing animals and wouldn’t do it themselves. Assuming you eat meat, do you feel or think you’re evil just because these people think you are? I strongly doubt it. You probably just don’t agree with them.
They’re working on an assumption (we’re animals too, and all animals have the same right to live than us) which isn’t utterly stupid. But most of us, and probably you too, don’t agree with this moral basic assumption. Note that nor you nor them can prove that the other is wrong. You just think/feel that killing an animal isn’t at all comparable with killing a human being, they think/feel there isn’t much of a difference.
Now, let’s suppose these people will eventually have their way (and I think it’s a very real possibility). If you were transported in this future society, 200 years from now, how do you think they would take you “carnivore” stance? Most probably, you would be considered in the same way than someone condoning slavery today. “How could you even consider for an instant torturing and killing a poor innocent calf, you wicked monster!”
Norms change, ideas change, morals change…