“This court has recognized that they have a high rate of recidivism and are very likely to do this again,” said the lawyer, Robert C. Montgomery, who was defending a North Carolina statute that bars sex offenders from using Facebook, Twitter and other social media services.

The Supreme Court has indeed said the risk that sex offenders will commit new crimes is “frightening and high.” That phrase, in a 2003 decision upholding Alaska’s sex offender registration law, has been exceptionally influential. It has appeared in more than 100 lower-court opinions, and it has helped justify laws that effectively banish registered sex offenders from many aspects of everyday life.

But there is vanishingly little evidence for the Supreme Court’s assertion that convicted sex offenders commit new offenses at very high rates. The story behind the notion, it turns out, starts with a throwaway line in a glossy magazine.

Justice Anthony M. Kennedy’s majority opinion in the 2003 case, Smith v. Doe, cited one of his own earlier opinions for support, and that opinion did include a startling statistic. “The rate of recidivism of untreated offenders has been estimated to be as high as 80 percent,” Justice Kennedy wrote in the earlier case, McKune v. Lile.

He cited what seemed to be a good source for the statistic: “A Practitioner’s Guide to Treating the Incarcerated Male Sex Offender,” published in 1988 by the Justice Department.

The guide, a compendium of papers from outside experts, is 231 pages long, and it contains lots of statistics on sex offender recidivism rates. Many of them were in the single digits, some a little higher. Only one source claimed an 80 percent rate, and the guide itself said that number might be exaggerated.

The source of the 80 percent figure was a 1986 article in Psychology Today, a magazine written for a general audience. The article was about a counseling program run by the authors, and they made a statement that could be good for business. “Most untreated sex offenders released from prison go on to commit more offenses — indeed, as many as 80 percent do,” the article said, without evidence or elaboration.

That’s it. The basis for much of American jurisprudence and legislation about sex offenders was rooted in an offhand and unsupported statement in a mass-market magazine, not a peer-reviewed journal.

“Unfortunately,” Melissa Hamilton wrote in a new article in The Boston College Law Review, “the Supreme Court’s scientifically dubious guidance on the actual risk of recidivism that sex offenders pose has been unquestionably repeated by almost all other lower courts that have upheld the public safety need for targeted sex offender restrictions.”

The most detailed examination of how all of this came to pass was in a 2015 article in Constitutional Commentary by Ira Mark Ellman and Tara Ellman, who were harshly critical of the Supreme Court.

Please read the remainder of this article in the New York Times.

Editor’s note: Melissa Hamilton (quoted above) will be a featured speaker at NARSOL’s June conference.

Writing for the majority, Justice Robert H. “Bob” Edmunds reasoned that since the statute under review in Packingham concerned only conduct, and not speech, the impact to registered citizens’ First Amendment rights was merely incidental to the otherwise legitimate interest of the state in prohibiting such conduct. He further reasoned that there were already “ample alternative means” through which registered citizens could participate in expressive forums open and available to them. His reasoning was strained and tortured and his opinion was summarily dismembered by the dissent penned by Justice Robin E. Hudson.

For additional information and analyses of what’s at stake for the community of registered citizens throughout the entire nation, please read Eugene Volokh’s piece in the Washington Post. Prof. Volokh teaches free speech law, religious freedom law, church-state relations law, a First Amendment Amicus Brief Clinic, and tort law, at UCLA School of Law and filed an Amicus Brief in support of the petition for Certiorari in the Packingham case.