Why not just change the wording of the maturity ratings, so it's more targeted. Ie, "Suitable for all ages" "Contains strong violence" "Contains coarse language" and that sort of thing, or a simple "recommended G+" "13+" "15+" "18+" to give visitors a better idea of how it compares to what they might watch on TV or whatever. I think maturity rating or filter is important, and can imagine if a parent visited the site to see if it was suitable for their child, and the first thing they looked at was an "18+" story, they might wonder if the whole site is only full of strong content, or if there is any stuff suitable for children.
As always, though, there will be younger people who read anything regardless. It's just like young kids going to a video store and hiring out Nightmare on Elm Street or something. Many people tend to read or watch what they want to regardless of whether it is suitable - but more conservative people would respect the ratings - especially if they could tell with a glance what the rating meant.