Incest is still illegal in the West. But whenever an incestuous couple is arrested, the reactions on social media represent a shift in attitudes on this descpicable act:

“These are two consenting adults! They love each other and that’s all that matters! Just because it’s disgusting to us doesn’t mean it should be considered immoral, much less illegal! They are not harming anyone!” But let’s stop and ask: Why is not harming anyone required for something to be morally permissible? What’s so bad about harming others? Sure, if we think about harming others, that might make us feel bad or even disgusted. It might cause us anger, but that doesn’t mean that it is immoral.

In moral philosophy, there is a theory of morality called emotivism. Emotivism says that our moral judgments are nothing but expressions of emotion. When we say, “X is wrong,” what that really amounts to and, hence, what it really means is just, “X makes me feel bad!” Of course, feelings are subjective — different people can and will feel different things about X. As such, anyone who attempts to make a factual claim like, “X is wrong as a matter of fact,” as if that is universally or objectively the case is simply making a category error. As an analogy, just because I don’t like the taste of coconut, for example, that doesn’t mean that eating coconut is wrong.

There are obviously many problems with emotivism. But it is interesting how liberals use emotivism for their purposes and use it selectively. For those moral proscriptions they disagree with, liberals jump straight to emotivism, e.g., “Incest is not wrong just because it makes you feel icky.” But for those moral proscriptions that they believe in, emotivism goes out the window, e.g., “Harming others is the very essence of immorality and something that we have to use the force of law to prevent.” The simple question is, why the selectivity? Why draw the line at this notion of “harm” (which itself is loosely defined and selectively applied)?

If you press liberals to explain why harming others is immoral, this forces them to get into the meta-ethical and metaphysical issues that they attack theists for. Either they have to dig in their heels and say it’s immoral because “it just is,” or they will just bite the bullet, reject the notion of morality in its entirety, and embrace what amounts to some form of nihilism. This can be responded to on its own terms but even absent that, to simply get a liberal to admit he is essentially a nihilist is itself a win that can be leveraged in further arguing against him.

This is how you play chess with these liberal humanists. Call them out for their atrocious selectivity and the checkmate will be close at hand.