One of the basic tenets of modern librarianship is that the freedom to read is an essential liberty. In 1953 the American Library Association and the American Book Publishers Council published a statement explaining why everyone should have the freedom to choose what they want to read, and no institution should interfere with that freedom.
“Every silencing of a heresy, every enforcement of an orthodoxy, diminishes the toughness and resilience of our society and leaves it the less able to deal with controversy and difference.”
It is because of these principles that librarians are almost always on the front lines in the defense of free speech, free press, and resisting censorship in all of its forms.
You can read the entire statement here.