I may not express this correctly
I know many viewers have decided that the rape scene, at least by length, is gratuitous. If you're mind is made up I won't try and persuade you, but I took away something different.
Rape is not a new subject to film, but it is rarely treated realistically in film. Most often it is completely invisible in a film, and only suggested by showing an imposing figure and then a cut away to a crying girl, or a shadow demonstration. We've all seen a ton of shots of a girl crying in a shower. There are numerous examples where directors have decided we're "mature" enough to see something violent, like zombies eating guts or soldiers being dragged around with missing limbs, and certain sexual encounters, even where rape is implied, but this is the one time I've ever been asked to look at what rape can truly, and often is, be. In the history of film I can think of few scenes as controversial as this one and yet I can think of so many scenes which are so much more gratuitous. Only this scene deals in rape. One would be hard pressed to suggest the scene is intended to arouse, and anyone suggesting it is exploitative would have zero precedent to build that argument upon. This scene says, if you choose to watch it's entirety, this is how a rape may go, all the way, from beginning to end. It is not romanticized, it is not metaphorized, and we are never asked to wonder if she enjoyed it. And finally, after all is said and done, when the act is over, instead of being lead through stylistic choices to decide how we feel about the rape, our own viewership forces us to confront it ourselves personally and (if you're smart about how to watch this movie) alone.
It's difficult to argue for art in rape. It's also hard to say that rape hasn't been treated "artistically"in many films, and this movie did away with any "art"ifice.