Filters block sites related to sex education, AIDS information, gay rights and abortion. Better filters break down banned sites by subject, and allow unblocking a site which has been incorrectly blocked. Although not perfect, they do a good job of filtering. Filtering does involve turning over selection of materials to outsiders, but libraries have relied on vendors to pre-select for years. It makes sense that vendors do not want to turn over valuable site lists.
Different filters handle banned sites differently.
Some allow people to view the stop list and change it, while others do not allow people to view the stop list, but do allow the stop to be edited. A filter makes a library's resources consistent with its mission statement. Libraries do not let users select the most appropriate materials. Users may select freely from whatever materials are available, but librarians through selection, restrict the choices. Internet resources are not unlimited, because blocks of time to use terminals are limited.