Shelf space in a school library is limited. Books should be chosen for the value they impart to student's education. If they are going to be offensive to parents who pay the taxes and send the kids to be educated, as a default that should be honored, or at least taken into account.
I wish that people did not object to Huckleberry Finn, for example. But I'm not a black parent whose kid comes home and says they just read a book in which the protagonist uses the N-word, and he's the hero. The few books in my school's library that talk about gun safety and hunting are so old, I have to think that publishers don't even send such books to libraries anymore, because of the superstition among many about guns being able to induce the bearer to commit acts of violence. No problem, my kids already know gun safety, having had to recite the rules before they got to go to the range.
Will this render school library fare plain and uninteresting and dumb down the books as far as critical thinking on controversial issues? No, doubt. But anyone thinking that the public schools are smartening kids up and teaching them critical thinking hasn't been to one in a while.