I understand the frustration. I made my tree private when I realized how much "junk information" is passed from tree to tree on this website and others by people who doesn't bother to authenticate the information.
That said, I find the private tree DNA matches maddening, too. I don't even bother to try to contact them.
To solve the conundrum, I downloaded my ancestry.com to FTM, removed all photos, documents and unverified "working" lines, and uploaded that as a new tree to ancestry.com, which I then linked to my DNA page.
I agree that the benefit of sites like this is what we can share.... I just don't want to sharing garbage. :)