This phenomenon occurs for a number of reasons explicated in the more detailed findings of fact supra. These include limitations on filtering companies' ability to: (1) harvest Web pages for review; (2) review and categorize the Web pages that they have harvested; and (3) engage in regular re-review of the Web pages that they have previously reviewed. The primary limitations on filtering companies' ability to harvest Web pages for review is that a substantial majority of pages on the Web are not indexable using the spidering technology that Web search engines use, and that together, search engines have indexed only around half of the Web pages that are theoretically indexable. The fast rate of growth in the number of Web pages also limits filtering companies' ability to harvest pages for review. These shortcomings necessarily result in significant underblocking. Several limitations on filtering companies' ability to review and categorize the Web pages that they have harvested also contribute to over- and underblocking. First, automated review processes, even those based on "artificial intelligence," are unable with any consistency to distinguish accurately material that falls within a category definition from material that does not. Moreover, human review of URLs is hampered by filtering companies' limited staff sizes, and by human error or misjudgment. In order to deal with the vast size of the Web and its rapid rates of growth and change, filtering companies engage in several practices that are necessary to reduce underblocking, but inevitably result in overblocking. These include: (1) blocking whole Web sites even when only a small minority of their pages contain material that would fit under one of the filtering company's categories (e.g., blocking the Salon.com site because it contains a sex column); (2) blocking by IP address (because a single IP address may contain many different Web sites and many thousands of pages of heterogenous content); and (3) blocking loophole sites such as translator sites and cache sites, which archive Web pages that have been removed from the Web by their original publisher.
Finally, filtering companies' failure to engage in regular re-review of Web pages that they have already categorized (or that they have determined do not fall into any category) results in a substantial amount of over- and underblocking. For example, Web publishers change the contents of Web pages frequently. The problem also arises when a Web site goes out of existence and its domain name or IP address is reassigned to a new Web site publisher. In that case, a filtering company's previous categorization of the IP address or domain name would likely be incorrect, potentially resulting in the over- or underblocking of many thousands of pages. The inaccuracies that result from these limitations of filtering technology are quite substantial. At least tens of thousands of pages of the indexable Web are overblocked by each of the filtering programs evaluated by experts in this case, even when considered against the filtering companies' own category definitions. Many erroneously blocked pages contain content that is completely innocuous for both adults and minors, and that no rational person could conclude matches the filtering companies' category definitions, such as "pornography" or "sex."
The number of overblocked sites is of course much higher with respect to the definitions of obscenity and child pornography that CIPA employs for adults, since the filtering products' category definitions, such as "sex" and "nudity," encompass vast amounts of Web pages that are neither child pornography nor obscene. Thus, the number of pages of constitutionally protected speech blocked by filtering products far exceeds the many thousands of pages that are overblocked by reference to the filtering products' category definitions.
No presently conceivable technology can make the judgments necessary to determine whether a visual depiction fits the legal definitions of obscenity, child pornography, or harmful to minors. Given the state of the art in filtering and image recognition technology, and the rapidly changing and expanding nature of the Web, we find that filtering products' shortcomings will not be solved through a technical solution in the foreseeable future. In sum, filtering products are currently unable to block only visual depictions that are obscene, child pornography, or harmful to minors (or, only content matching a filtering product's category definitions) while simultaneously allowing access to all protected speech (or, all content not matching the blocking product's category definitions). Any software filter that is reasonably effective in blocking access to Web pages that fall within its category definitions will necessarily erroneously block a substantial number of Web pages that do not fall within its category definitions. 2. Analytic Framework for the Opinion: The Centrality of Dole and the Role of the Facial Challenge
Both the plaintiffs and the government agree that, because this case involves a challenge to the constitutionality of the conditions that Congress has set on state actors' receipt of federal funds, the Supreme Court's decision in South Dakota v. Dole, 483 U.S. 203 (1987), supplies the proper threshold analytic framework. The constitutional source of Congress's spending power is Article I, Sec. 8, cl. 1, which provides that "Congress shall have Power . . . to pay the Debts and provide for the common Defence and general Welfare of the United States." In Dole, the Court upheld the constitutionality of a federal statute requiring the withholding of federal highway funds from any state with a drinking age below 21. Id. at 211-12. In sustaining the provision's constitutionality, Dole articulated four general constitutional limitations on Congress's exercise of the spending power.
First, "the exercise of the spending power must be in pursuit of 'the general welfare.'" Id. at 207. Second, any conditions that Congress sets on states' receipt of federal funds must be sufficiently clear to enable recipients "to exercise their choice knowingly, cognizant of the consequences of their participation." Id. (internal quotation marks and citation omitted). Third, the conditions on the receipt of federal funds must bear some relation to the purpose of the funding program. Id. And finally, "other constitutional provisions may provide an independent bar to the conditional grant of federal funds." Id. at 208. In particular, the spending power "may not be used to induce the States to engage in activities that would themselves be unconstitutional. Thus, for example, a grant of federal funds conditioned on invidiously discriminatory state action or the infliction of cruel and unusual punishment would be an illegitimate exercise of the Congress' broad spending power." Id. at 210.
Plaintiffs do not contend that CIPA runs afoul of the first three limitations. However, they do allege that CIPA is unconstitutional under the fourth prong of Dole because it will induce public libraries to violate the First Amendment. Plaintiffs therefore submit that the First Amendment "provide an independent bar to the conditional grant of federal funds" created by CIPA. Id. at 208. More specifically, they argue that by conditioning public libraries' receipt of federal funds on the use of software filters, CIPA will induce public libraries to violate the First Amendment rights of Internet content-providers to disseminate constitutionally protected speech to library patrons via the Internet, and the correlative First Amendment rights of public library patrons to receive constitutionally protected speech on the Internet. The government concedes that under the Dole framework, CIPA is facially invalid if its conditions will induce public libraries to violate the First Amendment. The government and the plaintiffs disagree, however, on the meaning of Dole's "inducement" requirement in the context of a First Amendment facial challenge to the conditions that Congress places on state actors' receipt of federal funds. The government contends that because plaintiffs are bringing a facial challenge, they must show that under no circumstances is it possible for a public library to comply with CIPA's conditions without violating the First Amendment. The plaintiffs respond that even if it is possible for some public libraries to comply with CIPA without violating the First Amendment, CIPA is facially invalid if it "will result in the impermissible suppression of a substantial amount of protected speech."
Because it was clear in Dole that the states could comply with the challenged conditions that Congress attached to the receipt of federal funds without violating the Constitution, the Dole Court did not have occasion to explain fully what it means for Congress to use the spending power to "induce [recipients] to engage in activities that would themselves be unconstitutional." Dole, 483 U.S. at 210; see id. at 211 ("Were South Dakota to succumb to the blandishments offered by Congress and raise its drinking age to 21, the State's action in so doing would not violate the constitutional rights of anyone."). Although the proposition that Congress may not pay state actors to violate citizens' First Amendment rights is unexceptionable when stated in the abstract, it is unclear what exactly a litigant must establish to facially invalidate an exercise of Congress's spending power on this ground. In general, it is well-established that a court may sustain a facial challenge to a statute only if the plaintiff demonstrates that the statute admits of no constitutional application. See United States v. Salerno, 481 U.S. 739, 745 (1987) ("A facial challenge to a legislative Act is, of course, the most difficult challenge to mount successfully, since the challenger must establish that no set of circumstances exists under which the Act would be valid."); see also Bowen v. Kendrick, 487 U.S. 589, 612 (1988) ("It has not been the Court's practice, in considering facial challenges to statutes of this kind, to strike them down in anticipation that particular applications may result in unconstitutional use of funds.") (internal quotation marks and citation omitted).
First Amendment overbreadth doctrine creates a limited exception to this rule by permitting facial invalidation of a statute that burdens a substantial amount of protected speech, even if the statute may be constitutionally applied in particular circumstances. "The Constitution gives significant protection from overbroad laws that chill speech within the First Amendment's vast and privileged sphere. Under this principle, Plaintiffs argue that the overbreadth doctrine is applicable here, since CIPA "threatens to chill free speech because it will censor a substantial amount of protected speech, because it is vague, and because the law creates a prior restraint . . . ." Unlike the statutes typically challenged as facially overbroad, however, CIPA does not impose criminal penalties on those who violate its conditions. Cf. Freedom of Speech Coalition, 122 S. Ct. at 1398 ("With these severe penalties in force, few legitimate movie producers or book publishers, or few other speakers in any capacity, would risk distributing images in or near the uncertain reach of this law."). Thus, the rationale for permitting facial challenges to laws that may be constitutionally applied in some instances is less compelling in cases such as this, which involve challenges to Congress's exercise of the spending power, than in challenges to criminal statutes. Nonetheless, "even minor punishments can chill protected speech," id., and absent the ability to challenge CIPA on its face, public libraries that depend on federal funds may decide to comply with CIPA's terms, thereby denying patrons access to substantial amounts of constitutionally protected speech, rather than refusing to comply with CIPA's terms and consequently losing the benefits of federal funds. See 47 C.F.R. Sec. 54.520(e)(1) ("A school or library that knowingly fails to ensure the use of computers in accordance with the certifications required by this section, must reimburse any funds and discounts received under the federal universal support service support mechanism for schools and libraries for the period in which there was noncompliance."). Even in cases where the only penalty for failure to comply with a statute is the withholding of federal funds, the Court has sustained facial challenges to Congress's exercise of the spending power. See, e.g., Legal Servs. Corp. v. Velazquez, 531 U.S. 533 (2001) (declaring unconstitutional on its face a federal statute restricting the ability of legal services providers who receive federal funds to engage in activity protected by the First Amendment).