So, 'Why is it "obvious" to us that the institution of slavery is an inexcusable evil?' (2003:166). This is the question once posed by another British philosopher, Stephen R. L. Clark. Given that it is neither obvious that nor obvious why slavery is wrong, I think the answer to Clark's question lies in the pronoun Clark uses: 'to us'. It is reasonable to interpret a false, yet frequently uttered, slogan in light of the social status of the persons uttering the falsehood—in this case, in light of Clark's 'us'. This is reasonable, because at least one function of frequently uttering a falsehood is the maintenance of an existing relation of social power. Who, then, is Clark's 'us'? Given the disproportionate predominance, in the academic discipline of Philosophy, of persons-classed-racialised-and-gendered-as-wealthy-white-men, Clark's 'us' is classed, racialised, and gendered in this very way. What, then, is the social relation of power maintained by the frequent utterance of the falsehood that it is obvious that slavery is wrong? Since the most recent incarnation of legal slavery unjustly put social power in the hands of persons-classed-racialised-and-gendered-as-wealthy-white-men, Parfit's Practice [i.e. treating the injustice of slavery as obvious] permits those persons who are predominant among professional philosophers (a) to place themselves on the right side of contemporary morality, while (b) putting paid to any discussion that might implicate them in the wrongness of slavery. This posturing and policing of philosophical enquiry constitutes racial injustice and oppresses persons who are racialised as black.
I'm not a racist, but I disagree with this. That is, I think it is obvious that slavery is wrong. But it is worth thinking about how we could show that it is.
Here are three approaches we might try:
1. We could analyse what slavery is, taking either the practice itself or the concept of it as the thing to be analyzed. Assuming we managed the task we would then have a set of components or ingredients that make up slavery, and we could, as it were, measure them for wrongness. If an essential feature of slavery violates the rights that belong to a rational being then we might hope to show in this way that slavery is unjust. But is it only rational beings that have rights? And what are rights? What grounds them? These are vexed questions. If, instead of rights, we talk about human dignity or value or sanctity then we face the same kind of questions. As long as we are talking about ethics we will inevitably (if we take this route) hit some kind of bedrock that is inexplicable: God, rights, etc. This need not be regarded as a problem, but it will always be open to our opponents to deny the existence of God, rights, etc., and some of this denial might be sincere.
2. We could try instead to be as concrete as possible, to avoid intellectually unsatisfying and all too easily dismissed references to God or rights or the kingdom of ends or higher forms of happiness or what-have-you, and focus instead on pleasure defined in terms of neurobiology. It might be, and might be demonstrable, that slavery is not conducive to pleasure understood in this way (not only for enslaved people for the population taken as a whole) and perhaps also that it increases pain (also understood biologically). There are reasons why we might not want to turn ethics into a matter of psychology in this way (or abandon ethics and replace it with psychology, if that's a better way of putting it), but it might be possible. It would be interesting to see what came out of it.
3. We could look at, or think about, the way that slavery fits, or fails to fit, with the rest of our lives. Instead of scrutinizing slavery itself we would look at the (human) world as something like a jigsaw puzzle or machine, and at slavery as a piece that might or might not fit into this puzzle. We might think about the various other ways we deal with human beings and about the various other ways we use the methods of slavery: beating, confinement, and so on. Is slavery a good fit with the rest of our lives? Does it cohere? Or is life with slavery incoherent in some significant way?
It is this third approach that seems most promising to me. But it will involve, so to speak, seeing that slavery does not belong in our world. There will be no explanation, because you can always make a piece fit. Doing so will involve violence, of course, but violence to a machine part or jigsaw piece is here just a metaphor for significant disruption of the flow of life, of the way we do things. And that is neither always nor necessarily a bad thing. That a given change is violent, a violation or spoiling of the previous order, rather than a radical improvement, is an aesthetic judgment. Not a simple "ooh" or "aah" response. It is a judgment. But it is an aesthetic, subjective judgment all the same. What is clearly wrong to a connoisseur might not seem wrong at all to someone else, although they could (at least in principle) be brought to see that it is wrong.
(This relates, I think, to Sean Wilson's idea of connoisseur judgement, and to Wittgenstein's saying that a musical theme is not just a mix of notes.)