Movies are too complicated to be subject to such arbitrary standards about the amount of sex and violence they contain. A movie that contains a lot of violence in a historical context is not necessarily inappropriate for older children, as in "Schindler's List." It's a horrifying movie because of the subject matter, but that doesn't mean older children shouldn't see it.
Agreed. Some movies are frightening or disturbing because of their subject matter, but I believe that everyone should see them at least once in their lives because of the moral lessons they teach, and because they're superbly made films. You mention Schindler's List; another somewhat upsetting but deeply rewarding and moving film I think all should watch is The Elephant Man. Actually, I think The Elephant Man too scary for all but the most precocious children (most kids would simply be horrified at the title character's appearance and miss the great humanistic message of the movie, which overpowers the horror aspect), but I would recommend it to a preteen or teenager without the slightest hesitation. I just have a real love for this movie. It's rated PG, by the way.