I don't think that the sex scene in Cold Mountain should be NC-17 rated 😖 well ok, it was a bit more than the usual nude stuff in such movies, but it really wasn't any worse than others
I generally disagree with the ratings and all, they do nothing, my parents allowed me to watch whatever I wanted and do my choices, and it didn't make me any less normal than other teenagers 😛
In fact, I have a friend whose parents are very protective, and they always forbid her to do stuff, so when she grew up, she revoluted hugely to do whatever they didn't let her do.
It depends on the child's maturity, and the parents' judgement, ratings are silly imho (well, there might be some cases in which they are needed, but generally I think we can live without it). If a movie is NC-17 rated, a 15 year old will wait for it to come out in VHS or DVD and watch it no matter what
and agreed, better watch sex scenes rather than violence, at least it will affect you in a better way 👆