"It's through sharing and comparing that many of these errors come to light."
I do share and compare. Apparently you missed the part of my post where I explained "I have never denied anyone access when they've asked - I always encourage communication and collaboration with other researchers rather than grabbing things from trees without even talking to one another."
"What if everyone was private?"
Then people would do more communicating before accessing each others trees. In my experience, making my tree private has encouraged people to contact me and collaborate more successfully than when it was public and people just copied things from my tree without even communicating with me.
Bottom line: my tree, my rules. Deal with it.