Another reason we need "Trusted Surveillance"
I can see "Anon" has already been given a good kicking for his naivete but I don't think you'll have changed his mind.
The first problem we've got is that "Anon" is more representative of the population than we are. And what the political class can get away with is largely determined by how many people will think like him rather than those of us who appreciate the dangers.
The second problem we've got is that we don't even know whether we can trust the initial allegation that the police have found a dna match at the scene of the crime. Although they have fairly reasonable "chain of custody" in modern forensics, they still do not capture the activities to a digital and immutable audit trail so such evidence could have been obtained illegally (for example at the time of arrest) and "planted" by corrupt insiders. When it comes to re-examination of cases more than a few years old, the chain of custody is meaningless so we have even less basis for trusting claims that a match has been found.
The third problem is that the way they maintain data on the National DNA database (NDNAD) is alongside the plaintext personal identifiers of the owner (Name and Address). This allows corrupt insiders to track individuals whose dna appears in various different places, to perform illegal searches on highly sensitive genetic implications arising from the sample data and to store that secondary data (albeit illegally) in a "profile" created for the individual.
The fourth problem is that once on the database - even if only because you submitted a voluntary sample to eliminate yourself from a "sweep" - you cannot remove your data.
All the above are prerequisites for totalitarian abuse. (For example the selection of individuals who have a genetic tendency to aggressive dissent - if ever we discover such markers - could be easily identified for "special treatment")
Granted we don't (yet) believe our present government is inclined to abuse the data to that extent, but governments are inherently inclined to abuse all the power they can get their hands on, so it is no more than prudent to ensure that they can't get their hands on this particular power.
None of which need prevent the full and voluntary registration of all citizens on the NDNAD. I've tried to describe how we could square this circle in my paper on ID Cards. http://www.fullmoon.nu/book/side_issues/IdentityCards.htm