You aren't required to use Facebook, you're free to use alternatives, but it's become so ubiquitous that having a Facebook profile has become necessary to participate fully in online life. (Think of the Facebook like buttons and "login with Facebook" options you see scattered all over the web, or TechCrunch comments, for that matter.)
To put it another way, why should people with legitimate reasons for using pseudonyms be forced into a ghetto? What kind of freedom is that?