At first I didn't like the idea either, but then I thought about something, and now I'm not so sure. People arrested (innocent or not) are fingerprinted. How is that different than DNA? In the context of modern times, a person's DNA is essentially their "fingerprint."
Finger prints and photo at booking are to confirm and document identity. I would even be fine with a retinal scan as a similar ID procedure. DNA contains tons more data than ID. At present we are still discovering new info contained in DNA. I for one have no interest in sharing that info with anyone without my permission or a warrant.