In the day and age of identity theft, many find the prospect of sharing their genomes to be frightening. Although I am not sure of the exact nature of their fears, as a genealogist it is frustrating when your second cousin is listed as an anonymous tester and doesn't respond to your contact.
The fear of being able to ascertain medical information from the matches is possible, however, to do so, someone would first have to know exactly where they match, search for the snp's relevant to medical information AND know their exact location on each chromosome, and then cross reference that to a match! Do you have any idea how labor intensive that is? Not to say there isn't some folks who would do that, but really, who wants to spend hours on that? The knowledge that would take on DNA is far above the average user.
I am a self proclaimed genealogy addict. I have tracked down relatives that are living and made contact by telephone, facebook and email. My expectation is never to necessarily forge a personal relationship, or to intrude, but to find information, verify what I have, and most of all, to ensure accuracy in my research. I don't expect most of the people I contact to necessarily be interested, or share my passion for family research. I only hope that they are willing to share their knowledge.
Testing my parents and myself was another step for me in my research. It was a way for me to hopefully breakdown some brick walls, and possibly find my half Uncles. It has been gratifying to confirm by DNA the accuracy of my research with DNA matches. To know that yes, I got it right. So when I see a match, and I reach out to them, my purpose is no different. I just want to figure out the connections. To see which 4th great grandparent this may connect to.
Sometimes we find however, what researchers call a NPE, a non parental event. Meaning that the person you thought was the father or mother, isn't. Is that disappointing, yes, but it is a fact that we as genealogists must face. Sometimes we find information that we don't want to find. Sometimes we find a relative no one knew about with DNA. But in genealogy, sometimes we find out that our great grandfather was in prison for murder. It may be easier to put our head in the sand and ignore it, but the truth is, we are all better for knowing.
I understand that there are many who have tested with 23andme or who have uploaded to gedmatch, who really aren't into genealogy. Maybe they are adopted. Maybe they are curious. That's okay. As someone who may contact them, it would be my wish that they be open to sharing what they do know. As someone who is searching for an adoptee, I truly hope that I can assist those adoptees that I match with. There is nothing more than I would like to do than to help them find some of their roots.
Now that I have been using DNA matches for a few months, I don't anxiously go to every match. Those 10 cM matches are just too hard to find unless they already match a known relative, or have a surname in common. I prefer to focus on the matches with more DNA. The chances are I may find something that way. What I have learned is more often than not, I will contact a match, and we will look at each other's trees, and nothing pops out. We may share a 74 cM match, but we can't find it. It's so frustrating.
Maybe that's why people don't share. I really don't know. Even on gedmatch, people post their genome, but leave no contact info. It makes you wonder why they bothered to put their data on there at all. I mean, yeah, we may be 4th cousins, but since I can't contact you, I will never know how. Maybe people are afraid that we will learn to much about them, however, the truth is, like most genealogists, I am more interested in your distant relative, than you. I want to connect the dots, figure out that great great grandmother's maiden name, or who that great great great Aunt married. It isn't personal, and it may seem selfish, but to be honest, the hundreds of hours I have spent researching is something that you may not understand. I, like so many others, willingly share all the fruits of those labors with anyone who asks. The information I ferret out, isn't mine alone, it is ours. It belongs to all who are my family, whether they are my first cousin, or my sixth cousin.
When I started genealogy, I never wanted a straight lineal family tree. I wanted a giant Redwood of a tree, with as many leaves and branches as I could possibly find. DNA matches, are such a great advantage to this.
So if you have tested, or are considering testing, be more open to the idea of sharing. You don't necessarily have to do anything other than share, and maybe tell the match your grandparents and where they lived. Because if they are any good at genealogy, your grandparents, as long as they were born before 1940 is all the information they will need.