Movie Style Ratings for YA Books?

So have you guys seen this? Basically there's some talk that there should be movie-like ratings created specifically for YA books. On one hand, I get it. I'm not a parent but I can get why parents would want a hand figuring out which books do and do not conform to their values.  There are alot of books out there so asking for  a simple way to look at a book and it's content isn't out of line.

But I think my problem isn't so much it being done, as it is how it would be done. Any rating system is going to be based around a list of flagged content, right? In movies its nudity, language, violence, smoking, drug use, etc. When it comes to books some board will have the job of deciding what deserves to be flagged. Langauge? That one is pretty cut and dried. Violence? OK, but how do you deal with the way violence is depicted? Is it action movie type glorification? Is it critiqued? Does it matter? And what about sexuality? Will hetero sex be flagged in the same way and to the same degree as gay sex, for instance? How about the way religion is handled in YA books? Could "blasphemous content"  become an issue thats flagged? I can sure bet there are people who would want it to be.

And once a list of flagged content is determined  how do we weigh these instances and arrive at a rating?

The MPAA, the group that does movie ratings, is frequently challenged for it's tendency to allow astonishing acts of violence in a PG-13 movie, but will slap an R on something that has a tiny bit of sex or a few bad words, no matter the context. Or, in another recent controversy the anti-bullying film Bully, a well reviewed film and an important one for our time, was given an R rating for using a bit of bad language. (As an aside, the MPAA is primarily made up of former big movie studio execs and, in what I'm sure is a total coincidence, the board tends to be much harder on indie films, even when they have similar content to studio films.)

And all of this brings us to the huge economic issues that will be at play. If a book is rated as being for more mature teen readers will B&N carry it? Will Target? Or Wal-mart?  Now, buyers may read a book and decide that despite challenging content it's an important book and deserves to be on their shelves. Once you start putting letter grades on things suddenly it becomes very easy for corporations to make a blanket statement that they won't carry anything with this or that rating, no matter the context. Saves them from being criticized. And once buyers say they won't take them you'll see publishers stop publishing them.  This ends nowhere good for books.

So in some ways I'm at a loss. I get some parents desire for this but I just can't think of how this can done in a way that doesn't get hopelessly tangled up in politics and doesn't ultimately hurt publishing and deny readers good books.

Any wisdom out there on this?