670 ASHCROFT v. AMERICAN CIVIL LIBERTIES UNION Opinion of the Court parental supervision or control." Congressional Findings, note following 47 U. S. C. § 231 (quoting Pub. L. 105-277, Tit. XIV, § 1402(1), 112 Stat. 2681-736). COPA presumes that parents lack the ability, not the will, to monitor what their children see. By enacting programs to promote use of filtering software, Congress could give parents that ability without subjecting protected speech to severe penalties. The closest precedent on the general point is our decision in Playboy EntertainmentGroup. Playboy Entertainment Group, like this case, involved a content-based restriction designed to protect minors from viewing harmful materials. The choice was between a blanket speech restriction and a more specific technological solution that was available to parents who chose to implement it. 529 U. S., at 825. Absent a showing that the proposed less restrictive alternative would not be as effective, we concluded, the more restrictive option preferred by Congress could not survive strict scrutiny. Id., at 826 (reversing because "[t]he record is silent as to the comparative effectiveness of the two alternatives"). In the instant case, too, the Government has failed to show, at this point, that the proposed less restrictive alternative will be less effective. The reasoning of Playboy Entertainment Group and the holdings and force of our precedents require us to affirm the preliminary injunction. To do otherwise would be to do less than the First Amendment commands. "The 'starch' in our constitutional standards cannot be sacrificed to accommodate the enforcement choices of the Government." Id., at 830 (THOMAS, J., concurring). B There are also important practical reasons to let the injunction stand pending a full trial on the merits. First, the potential harms from reversing the injunction outweigh those of leaving it in place by mistake. Where a prosecution is a likely possibility, yet only an affirmative defense is available, speakers may self-censor rather than risk the perils of