We agree that perverts in the street should be prevented from offering pornography to children. When we move the act into a government building and call it "Freedom of Speech," does it make it alright?
I think there is a difference between a living, breathing human being approaching your child and your child having access to a book on teen sexuality in a library.
What we CAN agree on is that public funding of libraries leads to conflicts like this. Why not just privatize the libraries, let the new owners decide what books to put on the shelves, and then customers can go to the library that best reflects their values.