It is up to the parents. If a parent took a child to see, "Kill Death Gore Raping of Children Part 2" and their child goes Jason Vorhees on someone, it's their god damned fault for doing that.
The directors are making a product, and it was the parents decision to expose the child to the product. Same goes with even Tobacco, if you encourage smoking at a young age (Lets hope you don't) and they get lung cancer, blaming the Tobacco companies is not one thing you should do.
Protecting the children, I am somewhat okay with, but in the form of Censors. FUCKING NO! I cannot stand Censors. They ruin everything, not just the experience, but the fact that somone's art now has limits. Imagine what would happen if they censored "The King's Speech". The entirety of film would suck (Possibly even the speech).
As for my "Okay with" part, Children should be gradually exposed to things, I mean really, at some age, probobly even 5, they will understand what alcohol is. Around 9-11ish they will be curious and find out what sex is. At which point, the parent must tell them in a simplified manner what it was. (At the age of 10, lets just say I found out what sex is through the internet, I didn't know how to delete internet history and got caught, my dad laughed and my mom gave me "The Talk" about what it was I looked at.) If a parent can't do this on their own, they are probobly not fit to be a parent.
Other people's enjoyment shouldn't be ruined to "Protect the Children".