The harm is: the parent here doesn't want to condone the language and/or the nudity. It is his/her right to do so.
Just because twelve year olds curse, doesn't make it "ok" necessarily. Lots of young kids get pregnant, too -- doesn't mean moms and dads should just accept it.
(And again, I WOULD bring my 13 year old -- but I respect another parents right to decide it is NOT right for their child/family.)
Personally, I am struggling with whether or not to bring my 13 and 10 year old to see n2n before it closes...not because of whether or not they will understand it but whether they will enjoy it. They know the music and love it, and they both REALLY want to catch it before it closes. But there is nothing worse than a bored 10 year old at the theater. (And since I'm a single mom living in Boston, I can't really bring one and not not the other.)
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.