How dangerous are the people on the registries? A state review of one sample in Georgia found that two-thirds of them posed little risk. For example, Janet Allison was found guilty of being “party to the crime of child molestation” because she let her 15-year-old daughter have sex with a boyfriend. The young couple later married. But Ms Allison will spend the rest of her life publicly branded as a sex offender.

Several other countries have sex-offender registries, but these are typically held by the police and are hard to view. In America it takes only seconds to find out about a sex offender: some states have a “click to print” icon on their websites so that concerned citizens can put up posters with the offender’s mugshot on trees near his home. Small wonder most sex offenders report being harassed. A few have been murdered. Many are fired because someone at work has Googled them.

Registration is often just the start. Sometimes sex offenders are barred from living near places where children congregate. In Georgia no sex offender may live or work within 1,000 feet (300 metres) of a school, church, park, skating rink or swimming pool. In Miami an exclusion zone of 2,500 feet has helped create a camp of homeless offenders under a bridge.

Make the punishment fit the crime

There are three main arguments for reform. First, it is unfair to impose harsh penalties for small offences. Perhaps a third of American teenagers have sex before they are legally allowed to, and a staggering number have shared revealing photographs with each other. This is unwise, but hardly a reason for the law to ruin their lives. Second, America’s sex laws often punish not only the offender, but also his family. If a man who once slept with his 15-year-old girlfriend is barred for ever from taking his own children to a playground, those children suffer.