I've oftentimes felt that the "Mature" rating is misinterpeted. It's meant to imply a mature player as opposed to mature subject matter in an abolute sense, since honestly it can be argued that extreme violence and graphic sex are not all that "mature" even if entertaining.
That said, people can go on and on about why people like some of the things we do. Sex, Violence, and being scared, sometimes all of them combined. Ask ten differant people and you'll probably get fifteen differant answers.
The bottom line is that there is a demand for such entertainment, however in viewing it you need an audience that can seperate fantasy from reality, and is unlikely to act impulsively on what they see. Teens have their own rating for content between kiddy fare and "mature" fare because they are able to seperate reality better than kids, but not as well as adults. They can for example tell when something is make believe, but they have a somewhat differant view on reality and understanding of how things work than adults which can cloud their judgement. For example I honestly do not think a teenager is capable of dealing with sex in an ADULT manner (and please note, when I say Adult, since even adults are arguably immature when it comes to sex, especially recreationally).
I believe it also takes someone who is relatively mature to be able to not only suspend their disbelief, but also suspend their personal beliefs for the purposes of entertainment.
To put things into perspective being scared, shocked or given the creeps is a negative experience. It takes a certain kind of person to be able to appreciate that (usually retroactively to an extent), this is why not everyone is a horror fan. You set out to experience horror, and the whole point is to offend you. One of the reasons why I am so open minded when it comes to content in general, especially in that genere. I feel the horror genere suffers because people frequently claim they want to see horror, but only want to see it on their terms which defeats the purpose. If you for example don't like satanism, rape, torture, mutilation, and gore, those are specifically the kinds of things it's going to take in order to shock you. Anything you find "acceptible" but it's nature is just going to be a cheezy laugh-fest funhouse experience in comparison.
At any rate, the bottom line is that "Mature" entertainment is not for everyone. Plenty of adults would be perfectly content with nothing other than "T" or "PG" type fare. That's fine for them, but there is a tendency for them to want to attack things they don't like because they simply do not get it.
Not a great answer, but those are my thoughts on the subject.
