If you are using Tor Browser in Tails over a coffee shop wifi while you are laying down under a blanket in the back of a truck driven by a stateless hobo with no fingerprints who you intend to murder later in a country with a healthy democracy, you are probably still not anonymous. If you are not doing those things, you are definitely not anonymous.
While a facebook account gives some legitimacy, I also like sites where you can post anonymously or at least pseudonymously.