I'm sorry. I understood you to be suggesting in post 2 that you were interpeting the provision to mean that "the states are only prohibited from doing what the Constitution expressly prohibits them from doing" in other parts of the Constitution. If what you are actually suggesting is that the Fourteenth Amendment should be interpreted to prohibit the states from doing what the Fourteenth Amendment prohibits them from doing, then you are of course correct and you won't run into any problems with that interpretation until you run into a real case.
In the real cases that will confront you, the statutes that you will be reviewing will not expressly provide, "The purpose and effect of this statute is to deny persons the equal protection of the law," or "The purpose and effect of this statute is to deprive persons of their life, liberty or property without due process of law." So when you attempt to review a real case, you will confront the need to interpret the meaning of the Fourteenth Amendment so that you can apply it to the particular facts presented. That will require that you proceed beyond simply stating that the Fourteenth Amendment "just forbids what it forbids" because that formulation merely begs the question - what does it forbid?
"Privileges and Immunities": All it's understood to mean really is that the state can't interfere with the relationship between the U.S. government and its citizens. For example, a your state would be prohibited from extraditing you to Iran on demand from the Ayatollah, because as a U.S. citizen, you have an immunity to being sent overseas to be prosecuted by a foreign tribunal, except in cases where an extradition treaty might apply, and even then it could only be under the auspices of the U.S. Department of State.
"Due Process": Ned said, "The statutes that you will be reviewing will not expressly provide...'The purpose and effect of this statute is to deprive persons of their life, liberty or property without due process of law.'" Even that unlikely hypothetical situation is a complete contradiction. There's no way a law can violate due process of law, because, "due process of law" means making sure you have a law to back up your actions against someone - in other words, not just throwing someone in the slammer because you consider him a "threat", or just plain don't like him. I know that courts have tried to twist it to mean that if you act on the basis of an "inappropriate" law, then due process is being violated, but that's nothing but a very sophomoric argument. That's what I mean when I said in post 19, that the 14th amendment isn't a blank check for judges to write their own legislation, even thought that's exactly how they've been using it.
"Equal Protection": This clause applies to how courts apply the law. A court would be in violation of it if it were to give someone a lesser sentence for a crime against another, on the basis of who the victim was, because then that victim would be denied his equal protection.
So the common thread running through all three is that they are simply prohibitions against the worst types of potential abuses of state power, not a blanket protection of unspecified natural rights. It's the job of the peoples of those states to make sure their own constitutions contain the appropriate protections, and ultimately, to make sure that their governments respect their rights.