The first thing I think we have to recognize is that the relativists are actually right about one point: When we talk about goodness and badness (not merely in the specific moral sense of “right” and “wrong,” but in the general sense of “desirable” and “undesirable” more broadly), we aren’t talking about some inherent property that the universe has, or that particular acts have. Properties of goodness and badness don’t just exist “out there” in the world, independent of anyone’s will. Acts can only have positive or negative value if that value is ascribed to them by sentient beings. If the world hypothetically consisted of nothing but rocks, and the wind caused one rock to roll down a hill and land on another rock, that event wouldn’t have any value one way or the other; it would just be something that happened. (By contrast, if the rock crushed someone’s foot, that person would certainly consider that a bad outcome.) The only way an event can be called good or bad (i.e. positive-value or negative-value) is if there’s at least one sentient being around to consider it good or bad. In other words, you can’t have value without a valuer.
That’s the part I agree with the relativists on: These kinds of valuations are necessarily subjective. The word “goodness” is basically just a synonym for “the positive value that we ascribe to things.” But does that then mean that we can never objectively say which actions are more good (i.e. have higher value) and which are more bad (i.e. have lower value)? On the contrary – as odd as it might sound, I think that subjective valuations are actually the very thing in which the objective goodness or badness of our actions can be grounded. Let me explain.
See, the key point here is that just because something is based on subjective valuations or experiences doesn’t mean that we can’t make objective statements about it. This is something we can see clearly enough when it comes to things other than goodness/badness, like our emotions and tactile sensations. Let’s say, for instance, that you burn your hand on a hot stove. The pain you feel from that experience is entirely subjective, true. But the fact that the pain exists is not. It’s not just a matter of opinion whether burning your hand causes you pain; it’s an objective fact that the universe in which you burn your hand contains more pain than an otherwise identical universe in which you don’t burn your hand. That’s not because painfulness is some inherent physical property of hot stoves; the subjective experience of hurting is what constitutes pain. But it’s because of that subjectivity-based definition that we can objectively say that some things are more painful than others. When we say that hot stoves are objectively more painful than room-temperature stoves, what we’re saying is that they objectively produce more of that subjective experience known as pain.
Similarly, take something like disgust. We can all agree that disgust is an inherently subjective valuation, not something that exists independently “out there” in the universe. The only way something can be called disgusting is if someone thinks it’s disgusting. And yet, it’s also possible to say that a hypothetical universe in which (say) everyone was asked to examine a bowl of vomit would objectively contain more disgust than an otherwise-identical universe in which everyone was asked to examine a bowl of roses. Despite the fact that disgust is a purely subjective valuation, we can nonetheless say objectively that certain universe-states will contain more or less disgust than others. Again, just because something is based on subjective valuations doesn’t mean that we can’t make objective statements about it.
And we can apply this same framework to the concept of goodness. Moral philosophers will often suggest that the only way to objectively ground the concept of goodness is to somehow find a way around the inconvenient fact that goodness seems to be nothing but a subjective valuation that we ascribe to things. But instead of trying to find a way around that premise, I think we can actually accept it as obviously true, embrace it, and run with it – and ironically, it’s precisely by doing so that we can form an objective basis for saying what’s good and what’s bad.
To illustrate what I mean, here’s one more thought experiment to go with the others above: Imagine a hypothetical universe in which (say) a mother noticed that her son was sad and gave him a hug; and then imagine a second otherwise-identical universe in which she stabbed him instead. In these scenarios, we can safely say that the inhabitants of the first universe (particularly the mother and son themselves) would ascribe a higher level of positive value (i.e. goodness) to the hug than the inhabitants of the second universe would ascribe to the stabbing. (Maybe if the mother in the second universe was a psychotic sadist or something, she might consider stabbing her son to be a good thing; but however much positive value she might ascribe to it, her son would certainly ascribe a whole lot more negative value to it – not to mention whatever negative value might be ascribed to it by the other inhabitants of their universe – so on net, the overall level of goodness ascribed to the stabbing would be significantly negative.) All of these valuations would be totally subjective, of course; the level of goodness ascribed to the mother’s actions by one person might be totally different from the level of goodness ascribed to them by another person. But what wouldn’t be subjective is whether the hugging universe ultimately contained a higher level of this subjectively-ascribed goodness than the stabbing universe. It inarguably would. What this shows, then, is that by accepting that goodness is nothing but a subjective valuation that we ascribe to things, we actually make it possible to make objective statements about which acts have higher levels of goodness than others.
Another way of saying this is that we don’t have an affinity toward certain things because they’re innately good and an aversion to other things because they’re innately bad; rather, our affinities and aversions toward these things are what constitute their goodness or badness. If we give something a higher level of subjective valuation, we can objectively say that it has a higher level of goodness, and if we give something a lower level of subjective valuation, we can objectively say that it has a lower level of goodness – because those subjective valuations are what goodness and badness are. Again, the only value that can exist is value that is ascribed to something by sentient beings like us. So if one action has a higher level of subjectively-ascribed value than another action, it’s necessarily better by definition, in the same sense that a triangle necessarily has three sides or a circle is necessarily round.
This might sound superficially similar to moral relativism; but it couldn’t be more different in its conclusions. Under moral relativism, there would be no basis for saying that (for instance) a society which routinely sacrificed children against their will was acting badly. Under this alternative system, though, if the society’s affinity for sacrificing its children was outweighed by the children’s aversion to being sacrificed (which it certainly would be, assuming the children were normal humans), we’d be able to objectively say that the society’s practice of child sacrifice was morally bad. (And assuming there were also negative effects on the broader society, this would be even more the case.) Weighing all the subjective valuations against each other would yield a total level of goodness or badness that we could objectively identify as positive or negative. And that’s the bottom line here: We can evaluate moral goodness as an objective quantification of individuals’ subjectively-held valuations and interests.