I think it is inaccurate and unfair to characterize private tree owners as rude and selfish and public tree owners as wonderful sharing people.
My primary tree was public for years and I shared freely until many supposed cousins copied inaccurately, creating error-laden trees.
My primary tree, with thousands of photos and documents NOT found on ancestry.com, is private. I keep a secondary tree, public, with links to all the records that are available online - not just ancestry, but other databases as well. I promptly answer ALL queries, even when the person sought is not found in my tree.
A distant cousin had copied many items for my tree. If he had asked, I would have given him access, when I took it private. Instead, he asked questions - about people not in my family, but in-laws of in-laws. I gave him what information I had, but politely reminded him that those lines were not in my family, but in his. He asked more questions. I then reminded him again, still politely, that these people were not my family. I received a tirade in return - in effect, that it was my responsibility to answer any and all questions since I had made my tree private.
There are nice people and not-so-nice people in any subset of society.