Why should we be moral?
At face value this is a trivial question. It just is, in part, what we mean by the word "moral" that we should be moral. Our concepts of morality, good and evil, right and wrong, virtue and vice, and so on, are normative concepts. It is analytic that moral properties give us normative reason to behave in certain ways. And so this question is something like asking why all bachelors are unmarried men, or why all triangles have three sides.
And yet, this doesn't quite feel satisfying. The question may still seem to raise an important challenge for moral realists to answer. I think this is only because of commonly held, unspoken assumptions that one has in their mind when considering the question. These assumptions make it difficult to say that we should always be moral. And so, when paired with what has been said above, these assumptions form a challenge to the moral realist. They might go something like this:
1. We should do whatever we have most reason to do
2. But if someone were to want to do something enough then they would have most reason to do it
3. Therefore, if someone were want to do something enough then they should do it
The first premise seems almost analytic itself. Normative reasons weigh for or against certain responses of agents. Often times different reasons aggregate to form an even stronger reason, or clash and cancel each other out. This is most clearly seen in the case of epistemic reasons, where each piece of evidence provides a unique reason to affirm or deny a theory. Whether or not we should believe the theory depends on how these individual reasons weigh up. The word "should", I take it, just refers to this sort of aggregate normative reason that weighs decisively in favour of some response.
But the conclusion (3) is in serious tension with a robust, non-relativistic form of moral realism. The robust realist would want to say that,
4. If something is immoral, then it would still be immoral (and would still be something we should not do) no matter how much we wanted to do it
From this and (3) it follows that,
5. Therefore, nothing is immoral
This, I think, is what motivates the question at hand. That, because of (1) and (2), we are trapped between moral relativism on one hand, and moral nihilism on the other. The question might be seen as a rhetorical move to prompt this realization. That second premise, then, will be a point of controversy. Many find (2) intuitive, but at the same time find (4) and (5) to be very unintuitive. So why not respond with a Moorean shift? A better defense of (2) is needed, and I think a compelling one can be given as follows.
2.1. There is no limit to how much someone can want to do something
2.2. Therefore, there is no limit to how much prudential reason someone can have to do something
2.3. But there is a limit to how much moral reason there is to do something
2.4. Therefore, if we want to do something enough (so that there is more prudential reason to do it than there is moral reason to not do it), then we will have most reason to do it
Premise (2.1) and the inference from it to (2.2) seems plausible. That someone wants to do something no doubt gives them prudential reason to do it, and the weight of the reason would be proportional to the strength of their desire.
Some might think to reject (2.3), but I am skeptical of this move. Moral reasons supervene on biological, psychological and sociological factors, such as health and happiness, fairness, liberty, and equality. Just as the weight of prudential reasons are proportional to the strength of ones desires, the weight of moral reasons seem proportional to the extent to which these subvening natural factors are being promoted or discouraged. At the same time, moral reasons appear to contribute only finite weight for or against some response. After all, things could always be worse. Murder is worse than theft, though both are immoral. But comparisons of this sort are meaningless between infinite magnitudes. Since such comparisons are sensible, and since the subvening natural factors are finite, it seems moral reasons must contribute only finite weight.
Others may think to resist the inference from (2.2) and (2.3) to (2.4), and suggest that at least some moral reasons just cannot be defeated by prudential reasons—no matter their relative strength. But this is rather odd, and demands explanation.
A more sensible answer is to just admit that morality is relative to prudence. But that relativism needn't go in any one direction. Many believe that God will punish all wrongdoers and reward the righteous in the afterlife. Similarly, some will argue that there are certain interests all humans have, in virtue of being rational agents or social animals, that are most effectively realized by being moral. If this is true, then we have decisive prudential reason to live a moral life and abstain from immorality. One can thus explain how it is that we should life a moral life, without even mentioning moral reasons. In this way, then, one can accommodate the relativity of morality and prudence without committing to a radical and unpalatable form of moral relativism.
Many find this compelling, but I am dubious. Relativism in either direction, morality being dependent on prudence or prudence being dependent on morality, doesn't strike me as correct. There are still counterfactuals that require explanation, such as: "Even if it were imprudent to be moral, we should still be moral." There is still a sense in which morality is non-relativistic, that these sorts of answers don't seem to be able to explain or accommodate.