I think people already could do what you say. You could be on Facebook and only have family and a small group of close friends that you share with. People don't

I think people already could do what you say. You could be on Facebook and only have family and a small group of close friends that you share with. People don't want that. They want to get as many likes as possible. They want to argue with people. They want to be voyeurs. Even something just as simple as group chat is available today. Why aren't people simply creating different group chats (or using GroupMe, e.g.) as their only sharing communication? They can control every level of privacy. I don't think people want that. They want max likes and they don't want to put any effort into it. They don't really care about privacy. If they did, they wouldn't share every meal and activity they do online.