Everything has its advantages and disadvantages. Same goes for Facebook. It could be used as a website to communicate with people of the same mindset. It could be used for the purpose to have people gathered to discuss something and conclude things in a constructive way, or you could sit all day long using Facebook, talking randomly without any clear purpose, and nothing else. That’s the negative side of it, but hey, it depends on the user.
So Facebook is not a waste of time, if it is used for constructive purposes.