Same as it would be if they showed "Schindler's List".
You do not show children things that are for mature audiences without having their parent sign off on it first.
I know this tends to confuse a lot of people, but they are not "your kids" and even if they are in your school your power over them is very limited.
Excuse me? I'm not the confused one here. These parents who put their children into public school and then complain about it are confused. I didn't send my kids to public school. But I was forced to pay hundreds every month in school taxes, leaving me to penny-pinch to feed and educate my own children until I had no choice but to sell our home. So, parents like this woman get zero sympathy from me.
I was only wondering what was wrong with the movie. The rating doesn't tell us exactly what's in the movie. But, never mind... I found another article that answered the question: It contains "graphic depictions of the murder of Emmett Till."