The majority of the Court rejected this argument, reasoning that since the Fourteenth Amendment draws a distinction between citizens of the United States and citizens of a state, the content of the Fourteenth Amendment Privileges or Immunities Clause, which specifically protects the privileges or immunities of U.S. citizens, must differ from the content of the Article IV Privileges and Immunities Clause, which protects the rights of the citizens of one state while visiting in another state. The federal privileges or immunities would not, therefore, replicate the basic liberty and property rights protected by Article IV. Instead, the federal privileges or immunities would be those that pertained to the Union as a whole, such as the right to petition the federal government. The Court’s conclusion here was contrary to the original understanding of those who wrote §1 of the Fourteenth Amendment. The net effect of this interpretation was to severely limit the utility of the Fourteenth Amendment Privileges or Immunities Clause. For a discussion of a potential resurrection of the Privileges or Immunities Clause, see Christopher N. May & Allan Ides, Constitutional Law: National Power and Federalism, §9.3.1 (6th ed. 2013) (the Fourteenth Amendment Privileges or Immunities Clause); and in this volume, §7.4 (“The Right to Travel”).
The decision in the Slaughter-House Cases had several significant effects on subsequent judicial interpretation of the Fourteenth Amendment. First, beginning in the late nineteenth century, the Court began using the Due Process Clause as a vehicle for incorporating various provisions of the Bill of Rights against the states. In this manner, due process came to signify something more than just a protection for procedural rights. The “selective incorporation” of the Bill of Rights continued throughout the twentieth century such that most of the Bill of Rights has now been incorporated into the Fourteenth Amendment. See §1.3. In this manner, the Due Process Clause has functioned as a partial surrogate for the moribund Privileges or Immunities Clause.
At about the same time, the Court also began interpreting the Due Process Clause as providing protection for substantive rights not necessarily found in the Bill of Rights. The liberty of contract, for example, was deemed a fundamental right that could not be invaded by the states without sufficient justification. Allgeyer v. Louisiana, 165 U.S. 578, 589 (1897). Again, this “substantive” approach to due process operated as a substitute for the judicially eviscerated Privileges or Immunities Clause.
Finally, in the late nineteenth century, the Court began to apply the Equal Protection Clause as something more than a provision for equal enforcement of the law. In Strauder v. West Virginia, 100 U.S. (10 Otto) 303 (1880), for example, the Supreme Court struck down a statute that prohibited African Americans from serving on juries. This interpretation of the Equal Protection Clause filled another gap created by the questionable decision in the Slaughter-House Cases by putting teeth into the concept of equality in the context of basic civil rights. In addition, the Court interpreted the Equal Protection Clause as applicable to all races, Yick Wo v. Hopkins, 118 U.S. 356 (1886), despite what one could characterize as the narrower focus of the specific concerns that led to the adoption of the Amendment. The scope of this antidiscrimination thrust was, however, limited by the separate-but-equal doctrine announced in Plessy v. Ferguson, 163 U.S. 537 (1896).
In short, by the end of the nineteenth century, the foundation for the modern law of the Fourteenth Amendment was established. That foundation consists of a combination of the text, the pre- and post-ratification history, the legislative intent, and a developing jurisprudence of interpretation and application. The foundation includes a commitment to the judicial protection of both substantive and procedural rights, as well as to an emerging concept of equality under the law.