Boudicah is concerned that she's sheltering her kids too much. I sent her an email as my reply was too long for the comments, and was asked to post my email to her here.
I'm twenty-two and I don't think that I'm old enough to watch South Park. I wasn't allowed to watch the Simpson's until I moved out of the house.
Kids today are confronted with a lot of things that I never had to deal with. I didn't even know the concept of homosexuality until I got to middle school. Now kids in Kindergarten are being taught that two moms or two dads is perfectly acceptable.
I think its one thing to understand that kids today are going to come into contact with shows like these, or games like Grand Theft Auto, whether it be through other kids at school or commercials on television. But by letting them watch these shows or play these games, we are sending our kids a message that at some level, these things are okay. There are fifteen year olds (heck, there are even a few of the college age) who can't discern these things properly, and as a result they become pretty messed up.
If your kids are in the public school system, then I would say that you don't need to worry about sheltering your kids, they are going to come into contact with it anyway. I think this means that if you find something to be inappropriate for your kids, then you have a duty as a parent to let your kids know, and to remain consistent with what you are saying by not allowing them to come into contact with it at home.
I think this in turn gives the child assurance that their home is a safe place and that if they need help they would feel comfortable coming to you with their problem. I realize that I'm not a parent, but I am a kid who was raised by great parents and looking back I can see the affect that that parenting had on me.