It is hard to dictate how every parent should raise every child, though SO many people try, especially online, passing judgement no matter what your decisions are. Personally, I don't agree with the rules of the ratings. I don't think swearing, nor sex, should be as big of an issue as violence. It's been proven time and time again that swearing has no little effect on a person's intellect, and even some articles proving that people swearing actually have a larger intellect and vocabulary. That's more a matter of teaching your child about 'proper place, proper time'. I swear all the time at home, but I also go on almost every field trip with my son, and obviously never swear then. I've talked to him about it, and pointed it out to him.
Same with sex. Children should know about sex (and, no, I'm not talking about picking up hookers on GTA5, or whatever). Sexual content is fine; sex is normal. And something I would hope would be part of his future. Better he knows about it and be informed than seclude him from LIFE.
Violence, however, is not something I'd want to see as being part of his normal life. Fantasy and playing games is one thing, but you need to make sure that they understand that it is fantasy, and not a way to treat anyone in real life. Even with that being said, I'll still never allow any GTA games in my home. This is not a point to create an argument. If you disagree, that's fine. People have different beliefs. I like pineapple on pizza, and some ass-hats want to go as far as making it illegal. I'm not saying to make the game illegal, but I have no interest in it being anywhere around me.
The biggest, most important thing, regardless of any ratings on games, movies, etc, is to be a part of your child's life. Don't pick up a game based on a rating and not find out about it. And talk to your child about what is appropriate and not appropriate. It's your responsibility to raise them and prepare them for the world.