Read some of the banned books on the list.
Some parents objected to the book sexual contents, other parents and adults object because the books are LGBTI friendly.
In a world that we need to teach children diversity and respect, parents are teaching children the opposite because of their religious or personal bigotry.
Following up reading.
Seriously. I lived in a place where people crossed border just to buy banned books. So don't ever take that for granted.