Everyone has the right to privacy. We also have the freedom to determine how much of our lives and our data we wish to keep private. You mention banks, etc. etc. – these are organisations to whom we have voluntarily given our information, making the judgement to trust them with it.
The trouble with ID cards and DNA databases is the fact that it’s government making them mandatory – you’d have no choice in the matter.
Now, when crimes are committed, freedoms are necessarily lost – part of the reasoning behind even the most extreme libertarian thoughts is that you have the full right to freedom as long as you don’t harm others in exercising that freedom. For example, the freedom to move (prison), to determine how to spend your time (community service), and also the right to your own privacy is lost when it is abused.
So when someone is found innocent of a crime, is it right for them to lose that right to privacy, with that DNA being stored without their choice?
Is it right for a victim of a crime to lose their right to privacy through no choice of their own? (and yes, if you watched some of the debates in the House of Commons, this happens).
You see, it’s fine to retain the DNA of a convicted criminal – they’ve abused their freedom and subsequently lose some of it, including their right to privacy.
But to retain the DNA of an innocent person, or to force them to use (and pay themselves!) for an ID card is fundamentally wrong.
As an aside, the biggest practical problems are these:
DNA and ID databases are open to abuse through corruption. Whenever you hear the word “government”, you’ve always got to remember that it’s some guy sitting behind a desk on a swively chair drinking coffee who’s actually got access to it
(NB I have nothing against guys sitting behind desks on swively chairs drinking coffee – the idea is to show that government is only as human and prone to error, mistakes and corruption as the people running it!)
People take bribes – people also give bribes. As with any organisation, these things are as mistake-prone as the people running them.
What if, for example there was a witness who had been granted anonymity and a vengeful friend of a convict gained access to the database?
These situations are well within the realms of possibility, and pioneers of the schemes themselves mention this as their greatest fear.
The other big problem with ID cards (in this case not so much the DNA database) is that it’s essentially a miniature poll tax – everyone, and I mean everyone, if it were to be compulsory, would have to pay £60.
(Worth noting once again that these arguments don’t apply if this is given voluntarily – but then making these things voluntary isn’t the point in them is it?)
[UPDATE]: David Craig points out in the comments that invoking the right to ownership of identity would make a stronger case than the right to privacy.