Our post-Civil War Fourteenth Amendment and civil-rights law is, in entirety, the only historical federal protection a State resident has from oppressive and unfair State laws. It holds three important protections of rights, including privileges or immunities, due process, and equal protection.
The latter two of the three clauses are rights, spelled out clearly and unmistakably, but they are not rights to privacy, religious freedom, property or speech. The rights are due process and to equal protection, intended to ensure just a fair and equitable legal process, but the the federal Supreme Court has many times stepped beyond this and overturned state laws or policies on far more broader grounds. Where do these protections come from?
Many scholars believe that privileges or immunities was the intended clause for protecting these greater rights, but a series of questionable Supreme Court decisions that may be grounded on something less than good law, rendered this clause useless and distorted the tiny due process clause so that it will perform great feats of which it was never intended and is impossible to do, if the term constitutional law means something.
The privileges or immunities clause was so limited by an early Supreme Court (Slaughterhouse cases) that it is never used anymore at all. A workaround was found by a Franklin Roosevelt 1947 Supreme Court. It applied a novel but unsound approach called "incorporation", using the due process clause to selectively "incorporate" Bill of Rights clauses into the Fourteenth Amendment so that theses rights may be applied and enforced against the States.
Everson v Board of Education rewrote the First Amendment so that we now have two First Amendments, one beginning "Congress" and the other "A state", and McCollum v. Board of Education just a year later used the newly created "amendment" to, for the first time, strip religion out of schools nationally. The Fourteenth had to be invoked twice, first to rewrite US law so that it applies to the States, and then to hold a state accountable for violating the newly created law. It is a twisted logic. The Court's action is, in and of itself, a due process violation; holding a state in violation of ignoring a law that did not exist until the time of the remedy.
The Everson decision mentioned only the due process clause, but certainly must have had the privileges or immunities in mind when it did it, but felt it could not use the clause because of the Slaughterhouse precedent. In fact, the same court in the same year applied that clause to a different case using the Slaughterhouse interpretation.
Later courts have depended on the Everson precedent to continue the dubious "incorporation" policy, and do this with the "magical" due process clause alone. Simply mentioning it is enough. It is magic. It can do anything, by court declaration, prohibiting student led prayers, overturning state law regulating abortion, and recently abolishing all state laws regulating deviant sexual activity, effectively ending or weakening the Founding Father's longstanding concept of "ordered liberty", the peoples' (and States') right to necessarily restrict some individual rights for ensuring the health and freedom of the whole. A simple right to due process does all this, single handedly.
Many scholars believe that the privileges or Immunities clause was for the purpose of "incorporating" the Bill of Rights into the Fourteenth Amendment, and while it's closer to the truth than is a stretching of due process, it will still amount to bad law. The Slaughterhouse Court understood this, realizing that rewriting US law so that it applies to the states will give unpredictable results, because of the different roles and associated powers of the two levels of government, and will collapse federalism with everything it touches, and by good law and sound logic, it should touch everything!
Thus, it would seem that the Slaughterhouse court got it right, but it's interpretation of the privileges or immunities clause has the seemingly well written and thought out phrase doing almost nothing whatsoever, leading legal experts to doubt this interpretation by the Court, and besides, didn't the amendment's authors want to extend Bill of Right protections to the separate States?
A privilege or immunity of a citizen of the United States would seem at a glance to apply the Bill of Rights to the states, but it cannot, and to try and do so will be bad law. Why? Because the Bill of Rights applies only to Congress, generally, and some clauses cannot incorporate, such as the 10th Amendment, where an attempt to do so would render state laws invalid.
U.S. citizens have an enumerated right to be protected from Congress abridging their speech, but not from a state. In fact, a privilege or immunity of a US citizen would be a right to regulate speech through his state government, a power given to the States by the 10th Amendment. Similarly, a US citizen will be free from fear of a national church but has a right to establish state religion through his representative state government. These are the privileges or immunities of U.S. citizens, or at least are the enumerated ones.
This interpretation of law is flawless. US law cannot change dynamically and thus no unpredictable results will occur. The clause may and should be applicable to every single federal law on the books. For example, if Congress passes a law requiring "Smokey bear" hats for park rangers and if this is seen as a safety related law for park visitors, then the privileges or immunities clause when applied will disallow a state from prohibiting Smokey hats in a national park. The supremacy clause will also handle this so the applying does nothing, or perhaps it may strengthen the Supremacy clause for peripheral areas, such as if a national ranger is on duty off of federal property. If a tough speaking state sheriff tells a national ranger: "You're in my jurisdiction now, take off that hat", the privileges or immunities clause may prevent it, U.S. citizens having a "privilege" of identifying their national rangers by the Smokey hat.
An "incorporating" of the same federal law may find a city park officials' "Smokey hat" requirement.
Many scholars believe the privileges or immunities clause must be limited to just the first eight Bill of Rights amendments or to selective Bill of Rights clauses, but, not only may this bring, and has it brought results never intended by the authors, it is also not what the law says. The clause does not say "first eight amendments", it says "privileges or immunities". A privilege or immunity of a US citizen is present in, or a basis of all or most federal laws, or otherwise the law doesn't have a purpose. The Fourteenth Amendment privilege or immunities clause, when applied to enumerated rights of U.S. citizens will generally only duplicate the supremacy clause found in the body of the Constitution. A focus on individual rights, rather than the law, will mean little, and the privileges or immunities clause under a Slaughterhouse interpretation will have little or no significance.. There may be a subtle difference between a right and a law, but it's unimportant because the clause is intended for greater things than the Slaughterhouse judgment found. It is important to note though that the Court's Slaughterhouse interpretation was correct, contrary to beliefs of some scholars; it just didn't go far enough!
We've covered enumerated rights and found that these rights in the Bill of Rights cannot be transferred to the States because it is not a privilege or immunity of US citizens to be exempted from state laws. The reverse is true. It is a privilege or immunity of US citizens to exercise their collective rights and regulate their society by way of the States.
Next come "un-enumerated" rights, mentioned in the 9th Amendment, and believed by the Founding Fathers to be the natural rights that citizens are born with, not granted by the government. Many of the Bill of Rights are such rights, enumerated. The privileges or immunities clause is for the purpose of extending a protection of these rights at federal level to all levels of government. The First Amendment right to free speech cannot be "incorporated" into the Fourteenth Amendment, but the right to free speech transcends enumerated rights and it is a privilege or immunity of a free people, and US citizens are such a free people. Thus, while the First Amendment may actually protect individual rights of state citizens to collectively regulate speech, a natural right to free speech protects United States citizens from oppressive state government.
What did the Fourteenth Amendment authors really want to do? At that time important civil rights legislation was making it's way through Congress and it was feared that a segregation minded court would strike the new laws down on the valid ground of jurisdiction.
Remember the enumerated rights argument above, the problem being that Bill of Rights protections targeting just Congress cannot be applied to the States. The dynamics changes though with US laws that target the States, and that, exactly was the intention of Congress, to target the states with new civil rights legislation.
A federal civil rights law prohibiting a state from denying the vote on racial lines, will conflict with contrary state law, and is applicable to the privileges or immunities clause, but Congress cannot create a new right that is not granted to the federal government by the Constitution. Therefore the Fourteenth Amendment must do more than overturn state laws conflicting with new federal civil rights laws. A new authority granted to the federal government could not be spelled out more elegantly than "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. "
An understanding and grasp that United States citizens have a constitutionally protected privilege or immunity to collectively control their communities and laws through their representative State legislatures, will bring new understanding to the Fourteenth Amendment and a renewed respect for "States' rights". United States citizens will regain their former privilege to the establishing of State religions, and will retain a federally protected privilege or immunity to the fundamental individual freedoms of religion and speech, to assemble, and so forth..
There will remain a fear of an overstepping of authority by the court,
because un-enumerated rights remain un-enumerated. In any case, a
confirming of quality judges is the only way of guarding against abuse.