In some ways, this is like a more extreme and 70s version of...

... Austrian auteur filmmaker Michael Haneke's 1997 film "Funny Games" and if you look carefully at the techniques used and metaphors, including the use of binoculars at the end as well as flipping them around, it is meant to be a criticism of audience in the violence it watches for entertainment and other purposes and shows its true horror.

Although "Salo" (1975) is indeed a more extreme and controversial version of that movie released 22 years later, but just watch the two and compare.