The immigration use of DNA profiling shows that it is inevitable that the Home Secretary will at some point profile DNA samples for propensity to crimes.
i.e. have X marker, means you'll be investigated for Y crime, because of a correlation between the two.
As you saw with Jacqui Smith's inability to distinguish between a causal relationship and a correlation, so DNA profiling is a correlation not a cause.
IMHO, the privacy right says there has to be a compelling reason to violate someone's privacy and that has to be balanced with the use.
When politicians have to pad the argument to keep innocent peoples DNA on file, it is a confession that they know the case isn't there to do it, and they just want to do it anyway.
It's a confession.
If there was a strong argument for keeping innocent people's DNA, then they'd make the argument and take everyones DNA. However the argument runs.... what harm can it do.... and on that basis try to take everyones DNA by stealth.
What harm can it do? My answer to that is two words: Jacqui Smith.