I can see from a 'pro' perspective that this would be a very good idea to deter many crimes. Rape, for instance, is known to be an opportunistic crime that goes up when the chance of being caught goes down - in war zones or aread of natural disaster, for example. A dns database would lessen instamce of opportunistic rape then, and maybe even child pornography where consent isn't such a thorny issue.
The major 'con' seems to be that at the moment we live ina liberal democracy, but at some point in future we cxan't be sure that the rule of law will change in line with a more hardline or totalitarian government, and that our DNA will be used to track people for non crimes, but mearly political agitation, etc.
What do you think?