The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. [4th Amendment to the United States Constitution]

• A national ID would violate the 4th Amendment. Demanding to see “papers” without probable cause would constitute and unreasonable and unconstitutional search.
• Because everyone (both legal residents and illegals alike) would be required to carry proof of legality, a national ID card would create an atmosphere in which all residents would be guilty until proven innocent. Currently, the police and other enforcement agencies must prove that you are here illegally; with a national ID card, you must prove that you are here legally. A government that views all its citizens as potential criminals is a hallmark of a Police State.
• A national ID card would destroy the right to privacy*, one of the foundations of individual freedom. The federal government would be able to collect and store data that is none of its business.
• The American people own federal buildings, national parks, and other public places; the government does not. Denying entrance to these places based on the ability to produce documents is unreasonable.

*For those who believe that the Constitution does not guarantee a right to privacy, please see the 9th Amendment:

The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.

In other words, just because the Constitution does not specifically grant a right does not mean that the people do not have it; enumerating all an individual’s rights would be impossible. Based on this amendment and the protections of the 4th Amendment, the Bill of Rights does indeed provide for a right to privacy.