This is very simple phenomenon to understand actually.
When a technology gets so mainstream that your parents and elders finally figure it out, be it facebook, Whatsapp, Twitter, Viber, Skype, then you should know your privacy has been compromised already.
The very fact that a parent doesn't allow his kid to use facebook should be a Big Red Sign for the kid to find something else.
Smart parents make smarter kids, because they always have to be two steps ahead of their parents. You can force him not to use Facebook, but he is going to figure out alternative in no time.
I am in huge favor of giving a child some "space" to figure things out, with right guidance off course. If he is learning from his friends at his school, that it should be a warning for parents to question to quality of that school and lack of judgment on their part to analyze the behavior trends.
False, misguided, and wrong use of technology is the core reason this thread exists. I am pretty sure 99% of users who saw early stages of internet learned to use it in three ways only, email, chatting rooms, and porn.