The US alone has a rich history of repression (Wikipedia even has a sub-subcategory specifically for ethnic cleansing) and it’s common knowledge those DNA databases have been used by US police to track people down so it’s really not difficult to link those two concepts. These are concrete examples of things the US government does or has done, not some hypothetical scenario.

And that’s all assuming the data is only accessible to governments that have to pretend to care about their citizens, not the for-profit companies and malicious actors that currently do have access to that data.