My mom is a children's librarian and in my experience the point of a library is to help kids and to get them to like reading, neither of which is silent. Reading to kids, teaching them, and helping them pick books are all primary parts of a library and none of them are silent. You can have specific sections set aside to be quiet as libraries should adapt to the communities they serve but saying that the purpose of a library is to read is taking an incredibly narrow view of libraries.