I think the R card is a great idea. Some kids are simply going to be more mature than others, and some people just don't think some "R rated" material is that shocking, compared to the real world. For example, the classic Do The Right Thing is R rated, but has much socially redeeming value for a bright 15 year old to grasp. While many R rated movies may just have pointless violence and sex, some of the best movies are R rated, because there is an assumption that if you're watching an R rated movie, you can handle complicated concepts. While you can do complex concepts on a G rating, film makers tend to assume that only films for kids can be G rated, which is sad IMO.