The issue to me is that without some assurance of privacy, you have no freedom of thought. For example, everyone has thoughts they don’t want others to know. Everyone is petty sometimes. Everyone has fantasies that they would not particularly want to share with all.
Everyone occasionally thinks uncharitable thoughts about a friend that they one the whole and otherwise love dearly. For example, “I wish she would stop dating only unavailable men, then maybe she wouldn’t get hurt.” You might think that, but you wouldn’t want it to get back to your friend.
People’s innermost hopes and dreams are delicate. They don’t particularly want them exposed to potential ridicule or judgment.