Public morality is among the oldest justifications for coercive law and one of the least disciplined. In Islamic legal discourse the problem is especially acute because a norm may be religiously obligatory or prohibited without the further proposition that contemporary public authorities may police every departure from it. The classical law of commanding right and forbidding wrong recognized coercive dimensions, but it also developed limits concerning visibility, privacy, knowledge, juristic disagreement, competence, and the likely consequences of intervention. Modern states alter the problem by joining those norms to legislation, police powers, digital surveillance, licensing, and administrative sanctions. This article asks when Islamic public law may treat individual conduct as a legitimate object of coercive restriction in the name of public morality. Through doctrinal analysis of classical sources, engagement with contemporary Islamic legal scholarship, and functional comparison with modern rights law and constitutional practice, it argues that moral wrongfulness is a necessary but insufficient ground of public coercion. State restriction requires a public-law translation of the underlying norm. That translation is justified only where the wrong is sufficiently determinate, has a legally cognizable public nexus, falls within a defined public competence, and can be addressed by a necessary and proportionate measure whose evidentiary basis and consequences withstand review. Privacy and valid juristic disagreement strengthen the presumption against coercion. The proposed public-wrong threshold preserves a meaningful role for public morality while denying the state an undifferentiated jurisdiction over personal virtue.