Your analysis is not complete, and you mean well but you have a fundamental misunderstanding of the nature of DNA collection in presenting it as a definite proof of guilt or innocence.
It is certainly not 100% proof. A match is often given as 1 in x million. When you consider the population of a country, then it means there could be 100+ other people who also match the sample.
Also, there is little to prevent the police from planting a DNA sample at a crime scene. It's easier to plant a sample than say, a handgun.
Also, the police are starting to use DNA as a way of tracking political activists and peaceful protesters. In the UK, the police are trying to build up a national DNA database, with samples from everyone in the UK. There's been much objection from judges and the public, but they are pressing ahead behind the scenes. Collecting DNA from UK schoolchildren in case they become future criminals is being seriously discussed at the moment.
I myself have refused to give a DNA sample to the UK police when I was arrested along with several others on a peaceful demo. They spent three hours persuading, threatening, and then just refusing to let me go until I gave a DNA sample, even though I was not charged with anything, and no reason was given to me for my arrest.
Under recently passed laws, I was forced to give them a DNA sample, with no option for refusing, even though the police agreed with me that I had committed no crime, that there was no crime being investigated, that I and the other arrestees were not under suspicion of anything.
They very much wanted a saliva sample, and I immediately offered them a hair sample, which is an acceptable substitute under the law. I was pressured for 3 hours to give them my saliva as for some reason they didn't want to take a hair sample. (probably as saliva is easier to process).
The DNA from that hair sample is now tied with my identity, and on any other peaceful demo or public assembly that I attend, if they do a sweep of the scene, picking up hair fragments, or skin cells from the ground, they will be able to identify that I and other named individuals were there.
If you want to see where this could lead, look at McCarthyism, and the current war on anyone who doesn't fit in. Also consider the massive government efforts on tracking peaceful protesters that continues to this day.
This is the current accepted State use of DNA in democratic western countries. Following our lead, what uses do you think countries like China are projecting for their own national DNA databases?
x RedTomato