Interesting discussion.
Personally I don't use Ancestry except for on occasion going to my brother's account (I'm listed as a user of his account.) to read something new he's discovered, or to add a bit of info.
My personal interest in our genealogy is to focus on remembering and documenting the stories of our family that my brother may be too young to have heard. For me, the stories about who they were and how they acted are more important to me than adding leaves. And also in encouraging my mother and aunts (now the three eldest in my family - with the exception of our newly discovered great uncle) to remember their stories.
Actually, that "add a leaf" thing DID work for my family on Ancestry. LOL they should pay my brother to make a commercial! My brother posted a picture of my grandfather and his fortunately unusual last name and it was found by my great-uncle that we never knew existed in Poland. And now two halves of our family have been very happily reunited. Uncle Kaz had the same exact photo of my grandfather, minus a crease that happened somewhere along Babcia's (Grandma's) travels.
And of course none of it would have happened if my Mom hadn't told me the truth about my father's father when I was 18 or if I hadn't later shared that with my brother. (Dad lied to us about his parental status all his life, even when confronted with the photo.)
So NOW both sides have an extended tree and we're all excited about it.
Granted this was (I assume) done with permission on both sides.
I understand wanting to keep your photos/documents to yourselves or at least to be asked/thanked/credited for your research. I also understand wanting to keep others from making stupid mistakes such as a relative who gives birth on both sides of the ocean within 6 months. I'm not sure what a cert is so I don't know how that plays in.
However for me, the idea of searching our genealogy is that the more brains and the more research that can link up, the better. So if any Adamski's or Cathers' or Bunell's want to share their trees or brain power I'd be all for a concerted effort! And I'm sure my brother would agree.
