People certainly have the right to make their tree private. No problem.
However, I would like to see a new rule. If a tree is private, then all other trees are defaulted to private for that person.
I recently had a potential 3rd cousin match in DNA whose tree was private. I asked to share their tree. Replied he prefers to keep private, ok. No problem. However, he began to explain to me that we had no tree matches, only one surname in 1700s and began to describe my tree. Of course, 3rd cousin DNA, quite plausible that one of us has a mistake and hence no match. But not the point. The point is this person has access to any public tree for his own private use, but doesn't allow public access to his.
Another example: I see people updating their trees with my stuff. Again, no problem. Heck I probably got from others too. However, I don't like when I click on the tree of the person accessing my data, and I get the private tree notice!
I want other public tree owners to see my tree. I don't want any private tree owner have access to my tree.
Ancestry! If a person has a private tree, default all trees for their eyes as private. I doubt we will have many private trees after this.