You can delete your dna after submitting it and viewing your results. Most dna sites have that option. Just curious, what are you afraid someone would do with your dna results? The government in America already keeps dna results on all babies born in the 80’s and later.
You have more to risk by joining NDMP to be a bone marrow donor, but in that case you’d probably want them to use your dna to find patients you could help. I honestly think everyone should join NDMP. I don’t work for them, or have anything to gain from their organization. I just think everyone should join and help people with cancer.