I agree that there should be a ratings system, however, I think it needs to be more defined. The MPAA should NOT run it! It should be judged similarly to court systems, by a group of unbiased anonymous people. Each rating should have specific criteria that defines the rating, and that criteria should be made public.
Each movie theatre and the ratings' organization website should have a more detailed explanation for the rating.
For example:
Rating: R
Curse words: 22
Sex: 2 sex scenes
Nudity: Female breasts and vagina
Violence/Gore: Guns, blood, exposed bones.
Other: sexual innuendoes, discussed descriptive intercourse, and more.
And then there can be the supplied more detailed list from there. This way, parents will know exactly why it got the rating it did.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle