Yes, I'm aware that, in theory, DNA is unique. As is the theory for finger-prints. But, I'm also aware that theory is rarely reality.
I don’t remember the exact details, because I have watched it long time ago, but they don’t need an exact match. Actually it’s more scary - if your distant cousin has DNA “in the system” - you are in it too.
This 1M DNAs may “help” match an order of magnitude more people.
I'd argue that while a DNA match could be a very good starting point for a conviction, other evidence should also be presented, for the reasons you suggest. For example, there is the case of the Phantom of Heillbron (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn), where European police found DNA evidence of a woman being at many diverse crime scenes, but it turned out the cotton swabs used for testing were contaminated by at worker at the factory (The swabs weren't certified for police work)
The problem is that we're proposing a DNA database, so you're now comparing 1 sample found at a crime scene with 300ish million people. That's a 300M in 100B chance, or 1 in 333, of some person having a false positive match.
Now combine that with thousands of samples being tested every day (because let's be honest, why wouldn't you use such a database for literally every single crime?) and you're looking at dozens of false-positives per day. It is only a matter of time before it isn't someone with an airtight alibi at the other side of the country, but someone reasonably-close who was just sitting alone on their couch at home all weekend. How are they going to prove they weren't involved in the crime?
This is why large-scale DNA matching is a horrible starting point for a conviction. It gives you a false sense of security, and it makes the investigators lazy. In most cases it is far better if DNA is used as the final nail in the coffin when you've already got a solid case against a suspect.
https://womenherald.com/health/the-chimerism-case-how-lydia-...
Your response is very uninformed at best.
In reality, juries often hold evidence like this (and also-very-unreliable eye witness testimony) in high regard, based on how it's positioned into the narrative.