(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie. Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")
Documents can and will be forged. If such a universal document were to exist, you can bet a large underground industry will develop to forge them. The industry already exists to forge drivers' licenses and state ID cards, but it is somewhat "mom and pop" in character. If a technologically advanced card is developed, organized crime will become involved, as the stakes (employment, social services, etc.) will become higher. Decades of nationwide narcotics prohibition have not prevented the widespread distribution of illegal drugs. Gun control has been ineffective in keeping firearms from criminals in places like Washington, New York, and Chicago.
The power of government has its limits. National ID cards will prove yet another failure.