How can someone possibly make a cost/benefit analysis when the future uses of public dna data are so speculative? Criminal in the 70s didn't think leaving their dna around could lead to their arrest 30 years down the line, probably didn't factor in their cost/benefit analysis at all. I guess maybe you could figure there's safety in numbers, if loads of people are in the same boat are you there's a ceiling on your risk (legislation eg). Those of us who grew up in the era of smoking a pack a day don't really feel that way.