While there is a multitude of moral theories, two of the big dogs of ethics are utilitarianism and deontology. John Stuart Mill presents the paradigm of utilitarian ethics: the morality of an action is dependent on the happiness and unhappiness it creates for the morally relevant beings. Moral status, for this sort of utilitarian, is defined in terms of the being’s capacity to experience happiness and unhappiness. Beings count to the degree they can experience these states. Obviously, a being that could not experience either would not count—except to the degree that what happened to it affected beings that could experience happiness and unhappiness. Of course, even a being that has moral status merely gets included in the utilitarian calculation. As such, all beings are means to the ends—namely maximizing happiness and minimizing unhappiness.
Kant, the paradigm deontologist, rejects the utilitarian approach. Instead, he contends that ethics is a matter of following the correct moral rules. He also contends that rational beings are ends and are not to be treated merely as means to ends. For Kant, the possible moral statuses of a being are binary: rational beings have status as ends, non-rational beings are mere objects and are thus means. As would be expected, these moral theories present two rather different approaches to the ethics of slavery.
For the classic utilitarian, the ethics of slavery would be assessed in terms of the happiness and unhappiness generated by the activities of slavery. On the face of it, an assessment of slavery would seem to result in the conclusion that slavery is morally wrong. After all, slavery typically involve considerable unhappiness on the part of the enslaved. This unhappiness is not only a matter of the usual abuse and exploitation that a slave suffers, but also the general damage to happiness that would tend to arise from being regarded as property rather than a person. While the slave owners are clearly better off than the slaves, the practice of slavery is often harmful to the happiness of the slave owners. As such, the harms of slavery would seem to make it immoral on utilitarian grounds.
It is important to note that for the utilitarian the immorality of slavery is a contingent matter: if enslaving people creates more unhappiness than happiness, then it is wrong. However, if enslaving people were to create more happiness than unhappiness, then it would be morally acceptable. The obvious reply to this is to argue that slavery, by its very nature, would always create more unhappiness than happiness. As such, while the evil of slavery is contingent, it would always turn out to be wrong.
Another interesting counter is to put the burden of proof on those who would claim that such slavery would be wrong. That is, they would need to show that a happy system of slavery was morally wrong. On the face of it, showing that something that created more good than bad is still bad would be challenging. However, there are numerous intuition arguments that aim to do just that. The usual approach is to present a scenario that generates more happiness than unhappiness, but intuitively seems to be wrong—or at least makes one feel morally queasy about the matter. Ursula K. Le Guin’s classic short story “The Ones Who Walk Away from Omelas” is often used in this role. There are also other options, such as arguing within the context of another moral theory. For example, a natural rights theory that included a right to liberty could be used to argue that slavery is wrong because it violates rights—even if happened to be a happy slavery.
A utilitarian can also “bite the bullet” and argue that even if such a happy enslavement might seem intuitively wrong to our sensibilities, this is a mere prejudice on our part—most likely fueled by examples the unhappy slaveries that pervade history. While utilitarian moral theory can obviously be applied to the ethics of slavery, it is not the only word on the matter. As such, I now turn to the Kantian approach.
As noted above, Kant divides reality into two distinct classes of beings. Rational beings exist as ends and to use them solely as means would be, for Kant, morally wrong. Non-rational beings, which includes non-human animals, are mere objects. Interestingly, as I have noted in past essays, Kant does argue that animals should be treated well because treating them badly can incline humans to treat other humans badly. This, I have argued elsewhere, gives animals an ersatz moral status.
On the face of it, under Kant’s theory the very nature of slavery would make it immoral. If persons are rational beings (and rational beings are persons) and that slavery treats slaves as objects, then slavery would be wrong. First, it would involve treating a rational being solely as a means. After all, it seems difficult to imagine that enslaving a person is consistent with treating them as an end rather than as a means. Second, it would also seem to involve a willful category error by treating a rational being (which is not an object) as an object. Slavery would thus be fundamentally incoherent because it purports that non-objects are objects.
Since Kantian ethics do not focus on happiness and unhappiness, even a deliriously happy system of slavery would still be wrong for Kant. Kant does, of course, get criticized because his system relegates non-rational beings into the realm of objects, thus lumping together squirrels and stones, apes and asphalt, tapirs and twigs and so on. As such, if non-rational beings could be enslaved, then this would not matter morally (unless doing so impacted rational beings in negative ways). The easy and obvious reply to this concern is to argue that non-rational beings could not be enslaved because slavery is when people are taken to be property and non-rational beings are not people.
It is, of course, possible to have an account of what it is to be a person that extends personhood beyond rational beings. For example, opponents of abortion often contend that the zygote is a person despite its obvious lack of rationality. Fortunately, it would be easy enough to create a modification of Kant’s theory in which what matters is being a person (however defined) rather than being a rational being.
Thus, utilitarian ethical theories leave open the possibility that slavery could be morally acceptable while under a Kantian account slavery would always seem to be morally wrong.