My friend, Richard Mouw, a philosopher and former president of Fuller Theological Seminary, has raised an important challenge  about the use of counterexamples when making one’s case on certain controversial moral and political questions.
He shares one of the arguments he employs to explain to his friends why he opposes the legal recognition of same-sex “marriage” (SSM): “If we are to operate as a society on the assumption that any sincerely held view about what constitutes a marriage should be granted status in our laws and practices, I have asked, what would keep us from legalizing plural marriages, or even incestuous ones?” Mouw says that his question is often “met with disdain,” with the retort, “[C]an’t you do better than a ‘slippery slope’ argument?”
He finds the retort frustrating, since, “some slopes are indeed slippery, and we do well to approach them with caution.” In other words, if you advance the truth of principle X in order to justify practice Y, something that you support, why not also accept practice Z, something that you reject, since it too is entailed by principle X?
So, for example, if you support the legalization of marijuana for competent adults on the principle that “one has a right to do whatever one wants to one’s body without directly harming others,” then that principle not only justifies marijuana legalization but also the decriminalization of hard drugs like heroin.
A person who resists this entailment by saying it’s a slippery-slope fallacy is confusing the fallacious form (often called a “causal slippery slope”) with the legitimate form of the slippery slope (often called a “logical slippery slope”). To point out that a principle entails something undesirable is not a slippery-slope fallacy. It’s an acknowledgment that principles have a logic of their own, so to speak.
Mouw goes on to write that he is in full agreement with the recent Supreme Court decisions concerning Hobby Lobby and Wheaton College: “In each case, employers have resisted health insurance arrangements that violate their sincere opposition to funding abortions. I share their views, and have argued that these sincerely held convictions ought to be granted legal status – which is basically the perspective set forth recently by the majority of Supreme Court justices.”
Now comes Mouw’s challenge:
Suppose a company owned by Jehovah’s Witnesses refused to support a health plan for their employees that permitted blood transfusions? Or what if a Christian Science employer refused to provide any health insurance at all? Surely those are sincerely held convictions that have a right to be considered for protection in providing employee benefits.The challenge is legitimate. And I don’t have an immediate response that settles the concern in any satisfactory manner. But I do take the challenge seriously. I have to – if I want the defenders of same-sex marriage also to take my challenge to them seriously.
First, the two cases are not symmetrical. There is no limiting principle even suggested in the case made for SSM by its advocates. The principles frequently offered are at such a high level of abstraction that it makes it next to impossible to exclude “marital” unions that people generally think ought not to be legally recognized, such as incestuous and plural ones.
In the religious liberty cases, however, there is a limiting principle, which is built into the law on which Hobby Lobby and Wheaton College have relied: the 1993 Religious Freedom Restoration Act (RFRA) . The part of the law relevant to our purposes here states: “Government may substantially burden a person’s exercise of religion only if it demonstrates that application of the burden to the person – (1) is in furtherance of a compelling governmental interest; and (2) is the least restrictive means of furthering that compelling governmental interest.”
This means that it is not the case that “any sincerely held religious belief” is an automatic trump to any generally applicable law. If the federal government meets its burden, then it may pass a generally applicable law that limits a person’s religious liberty.
Second, you can raise a turn-about-is-fair play reply: the counterexamples in the religious liberty cases do not address the question of whether the critic who uses them can provide a limiting principle on the federal government.
Here’s what I mean. Suppose a future Secretary of Health and Human Services issues a regulation under the Affordable Care Act that would require all qualified physicians and nurses in the United States directly to perform euthanasia, infanticide, abortion, or gender-reassignment surgery on any patient or close relative competent and legally permitted to request the procedure.
If you say this violates the religious liberty of certain physicians and nurses, guess what? Defenders of the regulation will trot out the Jehovah’s Witnesses and the Christian Scientists. In that case, the problem is not with advocates of religious liberty trying to figure out its limits, but with its critics, who have yet to offer a principled limit to the federal government’s regulatory powers through its administrative agencies.
Thus, it is the adversaries of our first freedom, and not its defenders, who have the slippery-slope problem.