The explanation behind the taboo behind rape/sexual assault versus acceptance of violence
Depiction of violence towards women triggers sadism in us much more effortlessly than other kinds of violence or torture. A recent study on correlation between violent videogames and violent attitude found no link between the two. But there are plenty of studies that show direct link between consumption of violent pornography and aggression towards women. Here is a meta study with tons of citations: http://aurora.umn.edu/pdf/ResearchOnPornography.pdf

Sadism is different from psychopathy. Psychopaths are apathetic, sadists are not. A recent study on sadism shows that sadists rated the pain experienced by the victim as more intense than the non-sadists did.

Inability to form emotional disconnection and higher awareness of the victim's suffering together can explain why we people triggered by sexual violence way more easily than non-sexual violence. From the famous Milgram experiment to very recent studies like this one:http://journals.sagepub.com/doi/abs/10.1177/0956797613490749 clearly show us that everyday sadism is very common. However, I don't know why sexual violence triggers sadism in us more easily than non-sexual torture.