Why Aren't Books Rated for Content But Movies Are?

People should be aware of the content in books before they open them.

  There should be a rating system on the outside jacket so one doesn't have to check the book's content before reading it.

It's the publishing company's job to create this system for their readers.

Remember:  Just because a book says says the content is for ages 12+, 13+, etc., doesn't mean that everyone thinks it's appropriate for that age.

Having a rating system, like films and tv shows, will help a reader decide if he or she wants to be exposed to said content.