I agree with all of you. Yes dna results can open cans of worms, and may not help you go further back, but also the reverse is true as well, and I've seen that occur,too. As to anonymity the U.S. companies- and esp. w/whom I'm familiar, i.e.-FamilyTreeDNA.com ...they do Not "store" any dna samples, and all are given "numbered" accounts, no names what-so-ever of the "giver" of the dna is recorded anywhere---one only shows the furthest back connection one knows---so as to "identify" that Line you descend from (such as:
"William Spencer, b. 1801, Egg Harbor, New Jersey, m. Susan Gilbralter" ,or some such statement). Also for the y-line dna (genetic) surname "marker" that only males carry, that's tested, That's ALL that's tested--ie- that's the oNLY part of the dna that is tested, to get the "surname" results. Then rest of dna left after the test is destroyed. So it's pretty darned secure--as nothing is stored. And they don't sell info or any type of thing to ANY 3rd parties.
But as you say, one Could possibly find-out about a "non-paternity" event in one's line, but it's Fairly rare (it does occur, but being what the penalties in the past for women who strayed, were, it's not all that common).
So is a useful tool for some. One lad I know who had been adopted at birth, but knew his birth father's last name was Spencer, did the Spencer group dna test via the familytreedna.com 's SHGS (Spencer Historical & Genealogical Society)'s (
www.myshgs.org) group rate test and DID Confirm his birth father WAS that Spencer man, and Did find out he belonged to the 4brothers Spencer group, out of Beds.c.1630 to America.
Other Spencer friends I had, who were NOT Of my particular Spencer group also took the same test via the route listed above, and they too found with Whom they belonged (other Spencer groups), but ALSO each of those un-related Spencers (either to me, or to others) were told What last Name THEIR Spencer clan had HAD before chaining TO that of Spencer generations or centuries before (in that name-changing I spoke of for the Spencer name as it related to a new position in life, that of a dispenser of goods/services). So THIS is the REASON i just Happen to know that THAT can and does occur, and did, with regards to the Spencer surname, not very often for any other surnames---but it Did occur in England, all over the place with the Spencer name, due many changing their careers and Wanted their last name to Reflect their new elevated position in society. It's sort of a unique thing that occurred because of the meaning of that word. So it's only due some of my un-related Spencer friends of mine, Telling me what They were told once their dna results came-in, that I became aware of this. It was NEVER published, nothing is told to the public of ANY of this- and in fact when i TRIED to post something on Ancestry.com on the Spencer posting boards, the wife of the SHGS's president at the time, got VERY Upset that I would publish any kind of Truth ABOUT the dna testing- as she did not want it known that most of the Spencers were NOT Spencers until a name change somewhere back in time. I don't see how it's any big deal---as ALL Families are iNTERESTING, their stories fascinating,
their People of WORTH, but a lot of people, apparently didn't want any kind of "truth" told, as it would maybe DIScourage folks from taking the dna test. Ok, that I can understand, as it would impact "sales", and also, I guess people Could become upset if they were told that, say, back 500 yrs ago, in the 1400s before you had the Spencer surname, you were, say, a "Cooper", uh, I guess that would be a problem, for some?!! Anyway there is what I know, but I still say that taking a dna test CAN often give one some valid information, as to relationships (folk have found close cousins this way, they didn't even Know of--as again, no paper trail- but when they compared their parents, grandparents, etc known info, they Found the link by talking, once they knew they WERE blood connected), and also dna can confirm or negate things you believe about your line, & show you IF you are on the wrong (or right) track in your sleuthing. So I say if there IS a "tool" to be used,why not give it a try? It might help!