Hey dumbasses you do know, the only thing the rape kits have are vaginal/anal/throat cultures of the VICTIM, and possible hair folicles. They dont go around testing people. 95% of the time police departments dont bother following up on rape cases, where the victim can't id the criminal, because they are strapped for cash, and cant afford to process the rape kits.
They then proceed to check that against the, database of convicted sex offenders...
I have no idea where you come up with the idea they are doing DNA tests at random, creating a national DNA database, etc. They are just testing evidence collected.