Earlier quoted context omitted.
I don't think one can expect privacy in a public place; the police can photograph you walking through a public park without a warrant. In fact, anyone has the right to photograph you in a public place. It seems to me that there is at least an argument that dropping your DNA in a public park is not very different.
You can absolutely expect certain kinds of privacy in a public space. (Like with up-skirt photos, for instance?) The question that needs to be resolved is if collecting DNA violates people's privacy in an unreasonable manner. I think this really falls back on the question of what harm you can do to someone with their DNA. The EFF apparently feels that you could do quite a bit of harm with it, if not today, then very…
I upvoted you, but I'll say for the record: this is an excellent point.