Maggie's Farm

"I had to look up The Incorporation Doctrine, but I am not sure that I fully understand it"

I don't either, but I understand at least some of what lies behind it.

The 14th Amendment reads in part, "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."

The three parts of this sentence are known respectively as the "Privileges and Immunities" clause, the "Due Process" clause, and the "Equal Protection" clause. Reading them in sequence, one would think that the "Privileges and Immunities" clause is the critical one in the Incorporation Doctrine. The rights in the Bill of Rights are clearly "privileges and immunities of citizens of the United States," so no state can abridge them. In the context of the time (post-Civil-War Reconstruction), it's clearly meant to counter the prewar doctrine that the Bill of Rights only limits the federal government, and give blacks some protection against state-level racist laws.

The problem is, in an 1873 case known as the Slaughter-House Cases, the Supreme Court read the Privileges and Immunities clause in a very narrow way that made it almost completely toothless. When the political situation turned around fifty years later and the Court wanted to find a way to bind the states using the Bill of Rights, it had to either overrule Slaughter-House or else find another way to apply the Bill of Rights to the states. For reasons I've never seen explained, it chose the latter. Thus we get Gitlow v. New York (1925), which uses the Due Process clause to "incorporate" certain rights by reasoning that violating those rights is contrary to due process of law. Later "incorporation" cases merely followed the Gitlow precedent.

By choosing this approach, the Supreme Court made two big mistakes. First, it set a precedent for twisting the plain words of the Constitution, which has caused no end of trouble since then. Second, it led to precisely the kind of tangle illustrated in the page you linked, where the justices have to argue over what constitutes due process and whether any specific right is included, and to what degree. An incorporation doctrine based on the Privileges and Immunities clause would be much simpler: all the rights are included, and bind the states to precisely the same degree that they bind the federal government.