Rather than writing much about this myself, I’ll just refer you Melissa Gira Grant, who knocks this AlterNet article out of the park.
For the last six years, police across the United States have been empowered by federal and state law to collect DNA from the people they arrest in order to build a government DNA database. The database includes those who have yet to face trial as well as people who are later found innocent. Now a group of researchers, law enforcement and conservative campaigners want to exploit people’s concerns about being included in such a database in order to scare people out of involvement in the sex trade. By threatening people with the possibility of being marked for life in a government database, these well-funded campaigners — with allies in law enforcement, including the Department of Justice — are using a questionably legal policing practice, a combination of “scared-straight” strategies that became a signature of the war on drugs and the extension of the surveillance state propelled by the war on terror.
Gira Grant touches on the constitutional questions, the financial incentives for law enforcement that come from targeting johns, the racial disparities in those targeted, the problems with the “science” behind the initiative, and the fact that targeting clients does nothing to improve the lives of those willingly (even if sometimes as the best of several unattractive options) in the sex trade.
(The only aspect of this she doesn’t dig into is the use of the Secondary Effects Doctrine, the idea that crime increases near sex-based businesses, to justify building such a database. It isn’t necessarily irrational to believe that the doctrine may hold where the sex-based businesses are already illegal–crime breeding crime–but in general, the doctrine and the scientific support it has received are not without criticism.)
Whether you consider yourself for or against the legalization of prostitution, I strongly suggest reading Gira Grant’s article.