Several Cato scholars, such as Walter Olson and Ilya Shapiro, have commented on the religious liberty and rule-of-law aspects of the Kim Davis case. In addition to their arguments, the Davis case is perhaps the clearest in modern times for a state establishment of religion.
Free Exercise is only half of the constitutional package of First Amendment religious protections. There is also the Establishment Clause, preventing the state or its agents from establishing a religion. It is a blanket anti-theocracy clause that is understood to be applicable to the states by the Fourteenth Amendment. As James Madison said on the House floor in 1789, the Establishment Clause seeks to stop a particular religion or sect from “establish[ing] a religion to which they would compel others to conform” or “enforc[ing] the legal observation of [a particular faith] by law.”
The key, under-explored factor in this case is that Kim Davis claimed “[the Christian] God’s authority” in denying same-sex couples the right to marry. By claiming “God’s authority” as the basis for denying the license—rather than any man-made law—Davis effectively established her religion in the Rowan County Clerk’s office and imposed on the religious liberty of those who hold other (or no) faiths.
People who do not subscribe to Davis’s particular brand of Christianity lose substantive rights guaranteed by the Constitution. That includes the right to civil marriage. Moreover, Davis’s establishment directly impinged on the right to freely practice any faith that accepts same-sex marriage, such as the United Church for Christ.
The right against establishment is just as important a protection for religious freedom as the Free Exercise Clause. Imagine if the Roman Empire had an anti-establishment rule. Christians pre-Constantine would have been able to expand Christianity without the threat of gruesome martyrdom. The right to be free from state-imposed religion is thus an important buttress to the Free Exercise Clause; without it, the state would always have a compelling interest in promoting its preferred religious uniformity at the expense of free exercise. That is a particularly undesirable result for a religiously diverse nation.
Regardless of what one thinks of the decision in Obergefell v. Hodges, same-sex couples have the constitutional right to civil marriage. Absent a constitutional amendment it is incumbent upon government officials to obey Obergefell. If that ruling conflicts with state officials’ consciences, their state duty not to establish their religion and impose it on others through state offices still trumps (when it comes to their official capacity—Ilya Shapiro wrote about the distinction between official and civil disobedience here).
The United States is a government of laws, not gods and men. Davis can quit, do her job, or recuse herself and let her office issue licenses without her participation, but she cannot claim God’s law as public authority to use her office to impinge on others’ rights and expect to be protected under the First Amendment. That is precisely the harm to liberty that the Establishment Clause was designed to prevent.