I cannot agree with you more. We are far too trusting of the government and its officers. Miscarriage of justice  and maladministration are widespread. The recent instance of a man, exonerated and released on appeal, being charged for board and lodging for the time he was held in jail shows just how insensitive the functionaries can be.   

It  is too easy to say it couldn’t happen here when we think of what the Nazis did. It could. Remember that their wholesale campaign of government sanctioned murder did not start with the Jews.  It started with true blooded Germans who were mentally or physically handicapped. Because the government  was trusted, no-one stopped them. They had proved to themselves that they could get away with it, so they moved on to the next undesirable group. 

We cannot predict the colour of the next government, or its taste for bigotry, and we cannot trust any government machine with the sort of power that a universal DNA database would provide.

Instead of making the database fairer by widening it, we should make it fairer by making it smaller.

First we should limit the occasions when it is legal to demand a DNA sample. Then we could allow the police (and no-one else) to keep and access DNA which has been legitimately taken from people against whom no charge was made, but for a period no longer than, say, three months. This should give them more than enough time to crosscheck against past crimes. At that point, they should be required to destroy all records. There could be provision for an exceptional extension of this period, under the supervision of a court, in cases of an ongoing investigations. Finally there should be a range of crimes and misdemeanours, such as less serious motoring offences, where the DNA would also be removed from the database after a fixed period.