Governmental DNA database

Um, would someone mind explaining what would be so bad about the government keeping a database of the DNA of all its people?  A safe storage of course, and only to be used for law enforcement.

I hear a lot of crap I don't understand like "Boo-hoo, I don't want the government to consider me a criminal in every crime ever committed :'''( *off to cut wrists. the wrong way*"

>>1
It's a good idea, but people shouldn't be forced to hand their dna over, it should be optional. If they ae a convicted criminal however it should be mandatory.

I think a simpler solution to solving all crime would be to have city walls and work around that.