I like the three possible morals to the story...
In the "happy ending" version, the moral is not to be a "chicken", but to have courage. In other versions the moral is usually interpreted to mean "do not believe everything you are told". In the latter case, it could well be a cautionary political tale: The chicken jumps to a conclusion and whips the populace into mass hysteria, which the unscrupulous fox uses to manipulate them for his own benefit, sometimes as supper.