The innocent have nothing to fear?
.For those who still believe, notwithstanding having read my previous articles regarding DNA, including one referring to the McCanns, that the innocent have nothing to fear from a DNA database I would just specify one potential illustration (although many others exist).
One aspect of the "CSI" effect is that people are now much more aware of forensic evidence and its potential. That includes disinformation. So there have been instances of professional criminals deliberately "muddying the waters" by scattering items which they will know will have DNA of the number of different people. They would do this to reduce the significance of any DNA emanating from them.
There is no reason to suppose that this will not be taken to its ultimate conclusion so as to offer evidence which might implicate other people.
Someone commits a murder in a city centre apartment. It is a planned killing, and the perpetrator takes great care to try and avoid leaving any fingerprints or DNA. We know that it is difficult to avoid leaving any trace, but it is certainly possible that any trace left would be difficult to establish with certainty.
In order to avoid the police concentrating on less compelling evidence, the murderer dropped something at the scene. It could be a cigarette butt, with saliva on it from the smoker from which DNA could be identified. It could be handkerchief which has been used to blot up blood from a shaving cut. There are any number of possibilities.
Obviously this will always be a possibility where it there is an attempt to frame a specific person. However suppose for the moment that the aim is not to frame someone in particular, but to draw the police away from the correct scent. Someone might have picked up a discarded item or more than one which could have DNA on them and then left them at the crime scene.
Let us suppose you had been having a cigarette and left the butt, somewhere in the city centre. The killer picks it up and then leaves it at the crime scene. You have never been in trouble, but your DNA is on the national database, because everyone’s is. The DNA is picked up from the cigarette butt. You are brought in for questioning.
You deny ever having been in the apartment, but your DNA is on something that was in there. Therefore in addition to being tied in forensically you'll be treated as a liar. You were in the city centre that evening. You cannot precisely account for your movements because you never thought you would have to. You will have no explanation as to how your cigarette butt could ever have ended up in the apartment. If you try and say that anyone could have picked up your cigarette butt then taken into the apartment, more than likely this excuse would be treated by the arresting officers with incredulity and rolling of eyes.
A national database assumes that DNA will solve crimes. In many cases it will, but if the starting point is to look for the DNA match against anyone whether they have been convicted of crime or not, it increases the chance that the first DNA match will be regarded as the main clue. This is the more so because it will always produce a suspect since everyone’s DNA would be there). If you found yourself in the position of the hapless smoker in the previous instance, I doubt you would still believe that the innocent have nothing to fear.