I would certainly argue that facial identification isn't necessary for domestic travel. It is none of the government's business where I go or how I get there; once airport security has established that I'm not carrying weapons, which doesn't require seeing my face of asking my name, they know everything they need to know.

For international travel, airlines are required to verify that passengers have the travel documents the destination country demands; as a result, they need to positively identify all passengers before they board the airplane.