I would welcome technology that could find criminals.. and hinder other crimes..
currently thousands of rape and other violent crimes sit unsolved, not for lack of evidence, but for a lack of test results,
illegals often take on many identities to thwart deportation and being nabbed for crimes, and should be tested as a way of seeing if they have committed a crime and if they have been deported a dozen times under other names..
as for the concerns.. if it is a good idea at stopping crime, then the ACLU will fight it forever, if they don't then I'll get concerned..