A few years ago, Marc Pepitone was arrested at a park in Bolingbrook, Illinois, a Chicago suburb, for walking his dog there. The problem was not the dog; it was Pepitone, who in 1999 was convicted of sexually assaulting a child, a crime for which he received a six-year prison sentence. A law enacted more than a decade later made it a crime for sex offenders like Pepitone to be present in "a park, forest preserve, bikeway, trail, or conservation area under the jurisdiction of the State or a unit of local government." Pepitone said he was unaware of that retroactive rule, but that did not matter: He was convicted of a Class A misdemeanor and sentenced to 24 months of conditional discharge, 100 hours of public service, and $400 in fines and costs. This month a state appeals court overturned Pepitone's conviction after concluding that the law he broke "is unconstitutional on its face because it bears no reasonable relationship to protecting the public."

The decision by the Third District Appellate Court of Illinois is unusual because courts generally defer to legislators' judgments about the best way to protect the public from sex offenders, no matter how dubious the judgment. The ruling is especially striking because the appeals court concluded that the park ban fails the "rational basis" test, a very permissive standard of judicial review. "To satisfy this test," the Illinois Supreme Court has said, "a statute need only bear a rational relationship to the purpose the legislature sought to accomplish in enacting the statute." That means "a statute will be upheld if it 'bears a reasonable relationship to a public interest to be served, and the means adopted are a reasonable method of accomplishing the desired objective.'"

Two other Illinois appeals courts have concluded that banning sex offenders from public parks makes enough sense to satisfy this requirement. "By keeping sex offenders who have committed offenses against children away from areas where children are present (e.g., school property and parks)," the First District said in a 2015 case, "the legislature could have rationally sought to avoid giving certain offenders the opportunity to reoffend." The Fifth District adopted the same reasoning last year. But the Third District argues that the rational basis test (which applies in this case because Pepitone made a substantive due process claim but did not argue that the park ban affects a "fundamental liberty interest") requires more than such an "incomplete and truncated" analysis. "While we acknowledge that under the rational basis test, '[a] statute need not be the best means of accomplishing the stated objective' and '[i]f there is any conceivable set of facts that show a rational basis for the statute, the statute will be upheld,'" the court says, "we also recognize that '[a]lthough this standard of review is quite deferential, it is not 'toothless.'"

The appeals court emphasizes the "overly broad sweep" of the law challenged by Pepitone, which imposes "an outright ban on all individuals with certain sex offense convictions from public park buildings and public park property without any requirement that anyone—particularly a child—be actually, or even probably, present." Because the law does not require any unlawful intent, it criminalizes "a wide swath of innocent conduct," including not only dog walking but "attending concerts, picnics, rallies, and Chicago Bears games at Soldier Field; or expeditions to the Field Museum, the Shedd Aquarium, the Art Institute, the Adler Planetarium, or the Museum of Science and Industry, all of which are public buildings on park land; bird-watching; photography; hunting; fishing; swimming at a public beach; walking along riverwalks; cycling on bike trails; [and] hiking at Starved Rock."

Dissenting Justice Robert Carter thinks the majority goes too far by expecting legislators to be fair or logical. "As long as the statute has a rational relationship to the government objectives, it is valid even if it is to some extent overinclusive or underinclusive," he says. "By keeping sex offenders who have committed sex offenses against children away from areas where children are present, the legislature could have rationally sought to avoid giving those sex offenders an opportunity to reoffend. Whether the statute could be more finely-tuned to accomplish that goal is a question for the legislature, not for the courts."

This dispute comes down to a question of what the rational basis test actually requires. In 2015 Kimberly Mueller, a federal judge in California, rejected a challenge to marijuana's legal status under the Controlled Substances Act, which she said easily passed rational basis review. "The law may be overinclusive, underinclusive, illogical, and unscientific and yet pass constitutional muster," Mueller wrote. Last year Phyllis Hamilton, a federal judge in San Francisco, quoted that same gloss while upholding the International Megan's Law, which requires special markings on the passports of registered sex offenders. A test that permissive is hard to distinguish from no test at all.