Actually, If I remember the recent reports right, there would be roughly 50 people in the world whose DNA signature would be indistinguishable from mine. So err.. yeah, not quite going to work yet that.
DNA evidence is properly used when it's part of a suite of evidence that is used to show that is is highly unlikely that anyone else could have committed a given crime/would be that person. DNA is not a form of authentication evidence, it's a form of elimination evidence. Plus it's actually significantly easier to steal a sample of someone's DNA sufficient to contaminate a scene than it is to do so with their blood for example, or even their fingerprints. What about monozygotic identical twins who literally do have the same DNA?
That's part of the problem with 'DNA evidence'. It's isn't foolproof on it's own and it probably can't be.
Plus such a database would be.. difficult to maintain. How many people are born every minute? How many die? who is going to look after getting them all on or taking them off the database? Who is going to make sure it's accurate? How gets to use it or not use it? what if your DNA showed you might get ill in the future; would a medical insurance firm be able to use that to charge you a higher premium even though you're currently in good health? What about paternity suits? How far does it go to being basically public knowledge?
It's an attractive idea but it's too flawed to base a universal, mandatory, trusted identification system on.
Jon
