Ratings for movies are nothing new. How ratings are determined, though, has been changing slowly over the years, and not necessarily for the better.
Movies with an NC-17 rating now are rated that way for supposedly too much sexual content. However, there is extremely uncommon now if not unheard of for a movie to be rated NC-17 because of violence. In fact, movies are pushing more violence than ever into the PG-13 category. People being blown up in war movies is allowed, but consensual safe sex, even in a very short scene with no inappropriate views, is not. Even gay relationships that don't have sex are highly censored and pushed into higher categories. I don't disagree with people who don't want to show children too much sexual content, but we seem to have no care about how much violence children see. While I think the research that claims consuming violent media makes children more violent is dubious at best (there are far more factors that play into violent lives than what the children are watching, playing, or reading), I think it's worth recognizing that Americans don't seem to care about the violence they're letting their children see.
Another thing wrong with the ratings system is that it highly favors companies and disadvantages independent films. An independent film is far more likely to receive an NC-17 rating than a company's film, even if the same 'blemishes' are present. NC-17 movies are almost never shown in theaters, and the restriction severely limits who is able to see the film. Because of this, independent movies are forced to have both less violence and less sexual content than an R rated movie would normally be allowed.
The last thing wrong is that the raters are random parents whose names are kept secret. On the one hand, the MPAA (Motion Picture Association of America) says that this is to keep the raters from bribes and harassment and things like that. On the other hand, it means consistency in ratings is not enforced, and the raters do not have to own any responsibility in how they rate a movie. Some of the raters don't even fit in the guidelines that the MPAA claims they fit, such as having children under the age of 17, because the raters stay raters for an undetermined amount of time. This means ratings will never even be re-examined as to how they could be better.
To me, the rating system needs to change. Personally, I think warnings of what is involved in the film is all that needs to be on a film, so that parents can easily and accurately judge if it is appropriate for their children to watch. Parents should be the ones deciding what their kids can watch, not random people who decide how much blood is too much or whether gay relationships are right or wrong. Parents also deserve to know exactly what is in a movie, not a vague label that could mean virtually anything at this point.
All of the information I have in this article is from the documentary "This Film is Not Yet Rated." If you want to learn more about the rating system and the movie industry, I suggest giving it a watch.