Considering watching this - input?

Most particularly, why the NC17 rating?

Henry and June was the first NC17 rated movie, and it received the rating for its sexual content. It would still, apparently, receive that rating if it were to be released today.

Other films receive the rating for graphic violence and brutality.

Way way back, Midnight Cowboy received an X, but the same movie today is considered an R. Same with A Clockwork Orange. Last Tango in Paris was originally released as an X, and is marketed as an NC17 today.

I've seen all of these films, by the way; I'm not squeamish or a prude. I'm just curious as to the "difficult" content of this film.

So what is it about this particular film that is so off-putting or dangerous that it earned this rating, which is generally considered the X of art films?

Thanks in advance.