Teachers and school librarians on trained in choosing appropriate books for their students and I trust their knowledge and judgement.  If a parent objects to a book they have the right to ask that their child read a different book.  As a parent I wanted my children exposed to books about different kinds of people including those who identify as LGTBQ+ because it develops empathy and insight into other's situations.  For a child who is considering suicide because he is not accepted, books may provide a safe space for him to learn that he is not alone.  We can't limit these books that can be life changing.