You might want to stay away from DNA tests if you or any of your close relatives have committed a crime. Although ancestry DNA testing companies don’t typically share database information with law enforcement, consumer DNA tests may result in future identification. For example, FamilyTreeDNA, which has a database of close to a million samples, has agreed to give the FBI limited access to the company's DNA database. This access consists mainly of consumer-level insights, like matches with other members of the FamilyTreeDNA community who have enabled family matching; by law, however, more in-depth investigation requires a subpoena.
Even the cousin matches seem to be based on the surnames listed in your tree with no attempt at comparing the people between trees to see if there is actually anyone in common! I have managed to find a few actual matches in the cousin match list, no thanks to their matching service, but more to the fact that I have been researching my tree for many years and am fortunate to know someone who is very competent at DNA and family tree research to help me weed out the rubbish from the genuine matches.
Newman says that there’s a basic lack of “literacy” and understanding about genetic testing, among the public and even other health professionals. People are given false reassurances or made to panic (just because you have certain genetic variants, it doesn’t mean that you will develop a particular condition). Newman also makes the point that, in his field, counselling happens before and after testing and, while people with cancer or heart issues nearly always opt to have the test (as they can then take action to varying degrees), often people with conditions such as Huntington’s disease in their family decide not to go ahead because a diagnosis would change nothing for them. In any event, Newman says that, with genetic testing, while there are different levels, intensive counselling is always “absolutely key”.