Comments on the United States Constitution (iii)
A brief further explanation of the basic flaws in both federal and state courts are in order. These courts are selected by the legislatures and executive whose power they interpret. This gives a strong selection bias (similar to adverse selection in economics, but involving the choices of third parties). When on the bench, operational bias (analogous to moral hazard in economics) biases verdicts towards increasing both federal power and the rights of other parties as narrow exceptions to those powers in order to increase the number and importance of disputes, and thereby increase the importance of the federal courts. The same logic applies to state courts interpreting the powers of state legislatures and executives under state constitutions.
An example of selection bias at work: you will almost always see Senators ask judicial nominees their opinion on the Commerce Clause. To be approved, the nominee cannot declare an intention to overturn preposterous interpretation by which "commerce among the States" includes growing marijuana or wheat in your own backyard for your own consumption. If a nominee does not declare allegience to this legal monstrosity, which has vastly increased the power of the President and Senate, most Presidents and Senates will not allow him on the federal bench. (The occassional joker, like Justice Thomas, does slip past both the President and Senate, but it's very rare).
Before the Incorporation Doctrine and the same-scope assumption, federal courts rarely enforced the Bill of Rights against the federal government. They enforced the small handful of limitations on the States in the original Constitution far more zealously. The combination of selection and operational biases produces this result -- the federal courts want to inrease their influence by enforcing rights, but have to commit to Senators (and often the President) who select them to not enforce them strongly against federal legislative or executive acts. They don't need to commit to States -- the States are not a source of selection bias -- so they can exercise their power freely by enforcing rights against the States.
Thus the federal courts have always been eager to enforce individual rights against the States, but very reticent to do so against the federal government. The Incorporation Doctrine and the same-scope assumption cause the federal courts to enforce the Bill of Rights against the federal government, going against their selection bias, as a price they are willing to pay to enforce a larger set of rights against the States.
A much better solution for keeping governmental powers in check and rights protected would be to have federal courts interpret state constitutions, and set up a new super-federal court, selected completely independently of federal politicians, to interpret the U.S. Constitution. Until such radical modification, the Incorporation and Same-Scope doctrines are crucial to incentivizing federal courts to enforce the Bill of Rights today.