The site in question, GEDmatch, does NOT sell DNA testing.
The user uploads their own DNA test results, from another company (Ancestry, Familytreedna, etc.) to GEDmatch for specific purpses. Voluntarily.
I have uploaded my own DNA test results to GEDmatch.
From the GEDmatch.com site today:
"April 28, 2018 We now have facility to allow users to
delete their registration/profile and associated DNA and GEDCOM resources. If you are interested in how to use this facility Click here to find more information.
April 27, 2018 To correct a BIG misunderstanding, we do not show any person's DNA on GEDmatch. We only show manipulations of data such as DNA matches
April 27, 2018 We understand that the GEDmatch database was used to help identify the Golden State Killer. Although we were not approached by law enforcement or anyone else about this case or about the DNA, it has always been GEDmatch�s policy to inform users that the database could be used for other uses, as set forth in the Site Policy ( linked to the login page and
https://www.gedmatch.com/policy.php). While the database was created for genealogical research, it is important that GEDmatch participants understand the possible uses of their DNA, including identification of relatives that have committed crimes or were victims of crimes.
If you are concerned about non-genealogical uses of your DNA, you should not upload your DNA to the database and/or you should remove DNA that has already been uploaded."
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As a long time genealogy enthusiast, and more recently DNA too, I come down in favor of the families of crime victims, the public at large, LEOs, versus the privacy of the murderers and their families.
Stated differently, serial killers should prevent their relatives from taking any DNA testing.