Comment by genewitch
Sure. Someone who has their data in 23andme was someplace where something horrible happened. Law enforcement has no leads, so they process the DNA, and find no matches. They subpoena 23andme (or just look at the leaked data, who knows), and that person is now a person of interest. If they don't know they should have a lawyer on their side with them when being questioned, they might talk themselves into prison.
Now imagine that person is innocent.
I know it's not exactly the point, but the answer is you always have a lawyer if you're being questioned by the police, especially if you're not the one who called them. This is in no way specific to any DNA related situation. If any law enforcement shows up and has questions for you, you say nothing until you have a lawyer with you.