The mark of the beast. A movie rated NC-17 will get very little publicity and not make it onto many screens. This rating hinders a director's creative talent. He must decide: Do I sacrifice art (NC-17) for money (R)? Very few directors make the right decision.
Requiem for a Dream by Darren Aronofsky was rated NC-17 and did poor at the box office. However, the decision made by him to keep it at the rating is a respectable one in that the movie very properly showcases the horrors of drug abuse in disturbing ways.