[Perishthethought]

Just because something has occured within the real world it doesn't make the rendering of it in an anime somehow more legitimate. Foursomes occur in the real world, but the addition of it into the anime somehow doesn't make it seem somehow more realistic. Ask yourselves why they included such graphic violence, why they had such a comical scene at the end. They certainly did not make this anime to somehow explicate the depths of madness or provide some sort of insight into the human condition. They did it to shock, nothing more, nothing less. The fact that so many people are left with an inability to decide how they feel about this anime is testament to the fact that it has deliberately confused people by throwing curve balls every step of the way, and the murders are no different, just the biggest of the lot.

Regarding the desensitising effect - that's completely intended. People were baying for blood because they wanted to people to readjust their attitudes to the players in erogames who try and bang every available character - they're despised when rendered in anime form. The violence and bloody conclusion was purposely over the top to reflect such an attitude. This is what I mean about various signifiers throughout the series in order to detach yourself and enjoy the fallout - the foursome was the most graphic. They were all meant to push you over the edge - they were the aforementioned curveballs delivered after such an immaculate beginning with the type of character development typical of the harem genre.

Just take a look at how different and above all, typical the first few episodes are there. The fact that they pulled it off with such aplomb should tell you something about the contempt they have for such the genre.