A game like Manhunt 2 even with an 18 rating will get into the hands of kids.
So does porn, that aint banned. So do 18 rated films, they aint banned. Kids go drinking under the age of 18, alcohol aint banned, kids smoke under age and fags aint banned.
There are in rules in place, hence certification, age ratings and laws. Its up to parents to enforce these upon their children, its not up to some big brother style agency to tell me how or how I cannot be entertained.