Why? Why do you honestly care?
Because it's a violation of my personal liberty!
Seriously, what next?
People are corrupt, we know. There would be measures put in place to limit it though.
Pfft. What if it's the government though? What's stopping them from using it to further their own corrupt agenda?
I absolutely hate to sound like a paranoid conspiracy theorist here, but if this sort of thing is allowed, there's nothing stopping the government from using the DNA to frame people who get in the way of their self-serving plans for crimes they didn't commit.
Now, this may not be so simple from a scientific perspective, from from a political point of view, the principle is very much there.
"They" could very easily get a sample from you from a discarded coffee cup.
They have no way of proving it's mine though, without, well, giving me a DNA test.
If they find DNA on a crime scene and it matches with my cofee cup sample, they can't say "Aha! It's SylvesterBr's DNA" "How do you know? we never got a sample from him." "oh, well, uh..."