Where, as here, strict scrutiny applies, the government may not justify restrictions on constitutionally protected speech on the ground that such restrictions are necessary in order for the government effectively to suppress the dissemination of constitutionally unprotected speech, such as obscenity and child pornography.  “The argument . . . that protected speech may be banned as a means to ban unprotected speech . . . . turns the First Amendment upside down.  The Government may not suppress lawful speech as the means to suppress unlawful speech.”  Ashcroft, 122 S. Ct. at 1404.  This rule reflects the judgment that “[t]he possible harm to society in permitting some unprotected speech to go unpunished is outweighed by the possibility that protected speech of others may be muted . . . .”  Broadrick v.  Oklahoma, 413 U.S. at 612.

Thus, in Ashcroft, the Supreme Court rejected the government’s argument that a statute criminalizing the distribution of constitutionally protected “virtual” child pornography, produced through computer imaging technology without the use of real children, was necessary to further the state’s interest in prosecuting the dissemination of constitutionally unprotected child pornography produced using real children, since “the possibility of producing images by using computer imaging makes it very difficult for [the government] to prosecute those who produce pornography using real children.”  Ashcroft, 122 S. Ct. at 1404; see also Stanley, 394 U.S. at 567-58 (holding that individuals have a First Amendment right to possess obscene material, even though the existence of this right makes it more difficult for the states to further their legitimate interest in prosecuting the distribution of obscenity).  By the same token, even if the use of filters is effective in preventing patrons from receiving constitutionally unprotected speech, the government’s interest in preventing the dissemination of such speech cannot justify the use of the technology protection measures mandated by CIPA, which necessarily block substantial amounts of constitutionally protected speech.

CIPA thus resembles the Communications Decency Act, which the Supreme Court facially invalidated in Reno v.  ACLU, 521 U.S. 844 (1997).  Although on its face, the CDA simply restricted the distribution to minors of speech that was constitutionally unprotected with respect to minors, as a practical matter, given Web sites’ difficulties in identifying the ages of Internet users, the CDA effectively prohibited the distribution to adults of material that was constitutionally protected with respect to adults.  Similarly, although on its face, CIPA, like the CDA, requires the suppression of only constitutionally unprotected speech, it is impossible as a practical matter, given the state of the art of filtering technology, for a public library to comply with CIPA without also blocking significant amounts of constitutionally protected speech.  We therefore hold that a library’s