Should books have ratings?

A book loving acquaintance bought the book “Brokeback Mountain”. She says that she’d rather read a book-turned-movie before she sees the movie than after she sees it. I agree with her. With the many award nominations for the movie, she intended to see the movie.

Trouble was, she did not know anything about the movie, nor did she read the subject headings, where she would have read the subject “homosexuality.” She was genuinely shocked by the book, and took it back to Barnes and Noble for a refund.

I asked her if her reaction would have been the same if she’d seen the movie. She said no, because she would have seen the ratings and expected it.

I wonder what would happen if libraries put ratings stickers on books like they do at the movies.