They are selling the data for (allegedly) medical research now. Tomorrow, they will sell it for genetic discrimination against you. The point is: it's not your data anymore, and from your perspective it can only be used against you.

While I understand there are pro-social uses of this data, such as medical research and identifying criminals and their victims, those exceptions should be clearly delineated by law in a white list, with strong safeguards, with the default being DNA privacy.