When it first came out, my first thought was privacy.
It's the single most immutable piece of information about a person. You can change your clothes, hair, face, address, phone number, driver's license, passport and SSN (a little harder, but doable), hell -- even your fingerprints if you really must.
But your DNA?
And you'd put it out on some webserver, voluntarily, as unprotected medical data?
it's so crazy to me how people just rushed to hand over their DNA to some random company
information about a person
Not only one person, but also their relatives, who didn't consent to begin with. You of course don't get all of it, but if you e.g. have the DNA of a parent, then you also get information about their children.
Say for example they have some genetic predisposition for an illness, then their child is probably also more likely to get it. Better hope that in the future there are still laws against using this kind of data for determining health insurance.
There's no way it's going anywhere good.
indeed
Highest bidder, probably insurance companies for blacklisting, or pig agencies for blackmail and emotional terrorism ("we want to find a relative of yours" .
Cast it into the fire! Destroy it! 
I have zero evidence for this, but I feel like JD Vance really really wants these data for some reason.