Hops,
Having been molested at age 9 and date raped at 17, I have devoted a lot of volunteer time over the last 20 years to sex education and awareness for parents and children.
I can't really speak to the Dakota Fanning issue, as I know nothing about the movie or what the message is that it is intending to send.  I would certainly not want my child performing in such a role, but that could be said of many child roles these days.
I do strongly agree that Brittney, Christina, Madonna and all of their ilk send a horrible message to our young girls who idolize them.  The clothing, body movements, demeanor and musical lyrics all scream sex and provocation--telling these young girls that if you want to be adored by boys, this is the best way to do it.  
I used to spend one day a month at my daughter's high school volunteering at the check-in desk.  I never left there without having been appalled by the apparel of at least a few of the girls.  Quite often there was more skin showing than clothing and nothing was left to the imagination.  I can't imagine what the parents are thinking when they allow their daughters to purchase such items, much less wear them to school.  Interestingly enough, many of the popular/cooler boys are very turned off by the outfits and behaviors of these girls--who are probably hoping to get the attention of those very boys.  They got it all right, but not in a good way and the boys put them in the category of sluts and skanks.  I do believe that if more decent, but hot young men would speak out against such behavior and clothing (I know, who am I kidding??), the message would have a better chance of getting through.
I know, I too am showing my age, but my 18 yo D is gorgeous, has a beautiful figure, but dresses in a modern, but tasteful way, and always looks adorable and just sexy enough for her age--so I know it can be done.
OK, I'm off my soapbox.
Brigid