The Kim Davis situation raises interesting questions about the meaning and practical effect of the freedom of religion. Although, for reasons that I will explain, the issue today is one of public policy, rather than constitutional law, the evolution of constitutional principles in this realm is illuminating.
The First Amendment forbids government to make any law "prohibiting the free exercise" of religion. At its core, this guarantee forbids government from intentionally interfering with the freedom of individuals to practice their religion. Thus, the free exercise principle at least presumptively forbids the government to enact laws expressly prohibiting Muslim women to wear burkas, expressly prohibiting Jews to circumcise their male children, or expressly forbidding Catholics to use sacramental wine. Such laws are paradigmatic violations of the free exercise principle, because their very purpose is to restrict the religious practices of particular faiths.
The Kim Davis situation is different. Consider, for example, a law that prohibits anyone to use peyote. Does such law violate the free exercise principle when it is applied to a member of a religious group that uses peyote as a sacrament? Or consider a law that compels military service. Does such law violate the free exercise principle when it is applied to a member of a religion that teaches pacifism? Or consider a law that prohibits discrimination on the basis of sexual orientation. Does such a law violate the free exercise principle when it is applied to apply to an elevator operator in a government building who refuses to allow in "his" elevator people he regards as sodomites?
The difference between the paradigmatic violations of the free exercise principle and these latter examples is that in the paradigmatic situations the laws at issue are expressly and purposely directed at the free exercise of religion, whereas the latter examples involve what is commonly referred to as the "incidental effects" problem.
In the incidental effects situation, a law that is not otherwise problematic on its face is claimed to be impermissible because, in application, it incidentally interferes with some individual's asserted "rights." This happens all the time.
Consider, for example, the freedom of speech. A law prohibiting speeding has nothing to do with free speech. But suppose an individual who is arrested for speeding insists that he should be exempt from the anti-speeding law because he was rushing to a lecture. Or, suppose an individual who is arrested for littering by dropping thousands of leaflets from a helicopter maintains that he should be exempt from the anti-littering law because this was an efficient way for him to communicate his views to others. Or, suppose a reporter who is arrested for burglary for breaking into a person's home asserts that he should be exempt from the law against burglary because this was a good way for him to get a story.
As common sense would suggest, in all of these examples the individual demanding the exemption will lose. Put simply, and except in truly extraordinary circumstances, the Supreme Court does not look kindly on incidental effects claims in the free speech context.
Why is this so? There are at least four pretty good reasons. First, once one opens the door to such claims, every tomdickandharry will assert them. "I robbed that guy so I could give money to my favorite presidential candidate -- Donald Trump." "I parked illegally so I could go to the bookstore." "I was naked at the beach so I could protest laws against nudity." And so on.
Second, in such circumstances, it would be next to impossible for courts to determine in each instance which free speech claims are sincere and which are a sham. It all rests in the mind of the actor, and everyone who does anything illegal would be tempted to cook up a free speech explanation. Sorting it out would be a fact-finding nightmare.
Third, even if a particular a claim is in fact sincere, and even if the individual did in fact violate the law in order to communicate, it would be daunting, indeed, to figure out in each instance whether the individual's free speech interest is sufficiently important to override the legitimate reason for the law. Is speeding to get to a lecture sufficiently "important" to justify speeding? Is being naked on a beach to protest nudity laws sufficiently "important" to justify the nudity?
Fourth, in most of these situations, with just a little creativity, the individual claiming the exemption could have expressed herself in some other manner, without violating the law. In such circumstances, the denial of an exemption does not significantly interfere with free speech.