Should Criminals Who Are Still Dangerous Be Kept Locked Up?

In her pieces for The New Yorker, journalist Rachel Aviv  follows subjects with complicated legal or medical problems, such as homeless LGBT runaways living with HIV, or whether teenagers who commit heinous crimes should be given life sentences.  
Aviv’s latest piece, “The Science of Sex Abuse,” looks at child pornography and civil commitment through the story of a veteran named John, a man convicted in the late 1990s of possessing child pornography and using the internet to persuade a minor to have sex.  
Once John was released from prison, he was again caught with child pornography and convicted of possession. Once he completed his second term, however, John was not released. Instead, he faced a  civil-commitment hearing, in which a Massachusetts judge determined that he was a “sexually dangerous person.” John was sentenced to the Butner Federal Correctional Institute in North Carolina, where he will complete a scientifically dubious program of treatment.
“Sex abuse is very hard to detect, and to prosecute, whereas child pornography use is much easier,” Aviv explains.
John’s civil-commitment judge could not determine if John had ever physically abused a child. As Aviv says, “There is this assumption that if you have these fantasies which you are expressing online, then you have also acted out on these fantasies, or maybe you will,” so the criminal justices system believes that perpetrators like John must be treated and detained.