The use in libraries of software filters to block constitutionally protected speech is inconsistent with the United States Constitution and federal law and may lead to legal exposure for the library and its governing authorities. The American Library Association affirms that the use of filtering software by libraries to block access to constitutionally protected speech violates the Library Bill of Rights . Publicly supported libraries are governmental institutions subject to the First Amendment, which forbids them from restricting information based on viewpoint or content discrimination. Libraries are places of inclusion rather than exclusion. The result is that legal and useful material will inevitably be blocked.
Filters can impose the producer's viewpoint on the community.
Producers do not generally reveal what is being blocked, or provide methods for users to reach sites that were inadvertently blocked. Criteria used to block content are vaguely defined and subjectively applied. The vast majority of Internet sites are informative and useful. As these products have moved into the library market, they have created a dissonance with the basic mission of libraries. Libraries are responsible for serving a broad and diverse community with different preferences and views.