First, some people extend your argument from DNA to everything and say "I believe that privacy in the modern world is unrealistic"; that doesn't make the argument applicable to the rest of us.
Second, whether DNA can or cannot remain confidential is yet to be seen, but feasibility is certainly orthogonal to whether it ought to be, which is the point at hand.
Third, whether you believe it's a breach of privacy to leak part of your relatives' DNA is besides the point. It's their decision to make, since it's their personal data and deemed confidential under most privacy frameworks, and therefore a breach.