My go-to is "what if literal nazis come to power and use this information to kick-start their eugenics program", but I guess rampant capitalism is also on the threat list.
In Japan there are maps of old caste demographics that are used to exclude categories of people based on where they’re from or their families are from from working - companies have been caught using versions of these maps that are illegal for businesses to use in hiring. They are legal to print or exist without being in use by business.