My personal view...
A video game, film, music or any other form of media will not effect a mentally mature person.
on the other hand a person still deveolping charactor is effected by anything around him being it actual life (parents behavior or friends) or media (tv, games all the sort).
I also don't agree with parents that decide that a rating is too strict for the 'kids'. If somethig is marked at 16+, this should not be shown to someone under age what ever the parent thinks.
The above reasoning is based on the following example: My wife being a teacher and studied child psychology and behaviour, can determine something being apropriate or not much better then a parent with lower scholar level.
I by no means think that someone is a more loving parent just cause of their intellectual level, but it helps making some choices. If you are not capable of understanding the consequences of you choices, you should stick to the markings.
Ow and I am totally against baning of any sort. Rate the item and spread to only eligible users.
The rating needs to be clear on what factors it is rating the media.