There seems to be two paths on this thread. There is the path of condimnation of the actions of an historical occurence and a path that examines how best to use background in a story line. I am pleased to see that we accept that the Nazi concentration camps did exist and that people (sub-humans and super-humans ) did act in ways that need to be condemned. Fascinating, is it not, that the Nazis would deprive themselves of one of the joys that experience by denying themselves the sexual/sensual side of their acts?
On the other hand, we enjoy a side of sensuality that the vanila world would definitely condemn.

I would think in terms of what I find enjoyable in a story. A big turn-off is the story where the impossible occurs. Think of the act of removing a hand yet having the victem continue of for several chapters without passing out or dying. Think, also, of the cop or cowboy in the movies who never seems to run out of bullets. A scene set in a plausible background is very appealing. A scene set in an impossible background is not. Naze stories where there is sensual/sexual contact have been destroyed for me now that I have been informed that the super-race would never have that type of contact. I think that those who enjoy that type of background as a part of a story or fantasy or story are looking that what can be believed as possible and that the story line is more enjoyable as a result.