[zeugma]

If you don’t want the police to use it to solve cold cases, don’t submit your DNA to GEDMatch.

That won't really help. If your sister decides to submit hers, unless you're adopted, they can certainly use that for correlation.

[centurion316]

No doubt, that’s the way DNA works. The genie is out of the bottle, while you may have some control of your DNA, you have none for the DNA of your sister or cousin, and the feeble attempts to write laws to do this will fail.