Who is this "we"? Government? We have free speech rights so government has no say. What the pilot can talk about is up to his employer. Which brings us to....
Who needs governmental prohibition on free speech, when you've got business to do it for you?
The airline as much right to fire the pilot as Jim Robinson has to ban people from this board and for the exact same reason: You have the right to free speech, you have no right to compel someone to provide you a forum.
The pilot called some of his paying customers crazy, for nothing more than their closely held personal beliefs. He has every legal right to do so, and his employer has every right to send him home.