I don't really see the moral difference between reading about somebody raping someone else, and someone strangling another person with barbed wire (which is mentioned in the HH series). They both appear on the surface to be equally brutal and horrific acts that no sane person would ever want to experience or read about. The *only* reason Rape is more shocking than murder is because society freely talks about murder every single day - there is nothing intrinsic in the act to make it more or less reprehensible than any other crime/sin/whatever.
I would disagree that it's the only reason - I find rape more shocking due to the intent and motivation behind it. Murder can be motivated by so many things, and it can be painted as heroic, justified or necessary, especially in a fictional setting. You cannot apply the same motivators to rape in any setting, which is why I think the two should be considered separately.
I'll agree that some of these views are enforced by society, but do not stem from it.
I defy you to find a better or more masterfully encapsulated depiction of Rape in any art form.
If you feel this diorama encapsulates rape for you, then i won't argue with you. I'm just saying that personally i find it quite bland and unnecessary. It's broaching a subject that has no place in 40k, which as you say is a virtually sex-less environment.
When i think of art which depicts rape, i'd think of something like Irreversible, which i found difficult to watch and made me sick to my stomach.