this is what happened...

in the US there used to only be X-ratings (or XXX, but i don't know what the difference was)for films that were considered to be beyond what anyone under 17 should see. rarely was anything other than pornography released with an X rating.
the industry decided that there needed to be a rating for films that were beyond R,especailly in violence, but not with the stigma of an X rating, so they came up with the NC-17.

so what happened?? the big theatre chains and advertising outlets ruined the whole plan by not showing, or adveritising, films rated NC-17. so we ended up in EXACTLY the same place that we were before, no rating that declares a film acceptable to the general adult public, but not for kids. plenty of films, i'm sure would have been released as NC-17 if the theatres would have shown them, but they were cut down to get an R rating. the one that comes to mind first to me is Casino. Scorcese had to cut down the scene with the vice to get an R rating.

so what we have is the MPAA and the theatre owners telling the genius how to make films....isn't that great...???