Have you heard about the movie Bully?
It's a documentary about peer-to-peer bullying in schools, and is directed at American youth in middle and high schools. Unfortunately, some of its content is charged with violence (hardly surprising, given its topic), and it earned an MPAA rating of R. Despite the filmmakers' appeal to change the rating to PG-13, which would allow its target audience to actually see the movie, the R rating stands.
So it will be released without an MPAA rating, which means theaters have the option of whether to allow children to see it. Not all will.
According to The Mary Sue, the rating decision was tipped by only one vote. Which begs the question, where is the line, here? Fictionalized violence on the same level or worse gets PG-13 ratings. Why make a movie about a real issue so inaccessible?