Moral realism is the view that there are objective moral facts about the world. By "objective", we mean that there are moral propositions which evaluate to true or false independently of people's opinions. A paradigmatic example:
"Recreational baby torture is wrong." This statement is a moral proposition about the world that has an objective answer (either true or false).
From Wikipedia:
Moral realism (also ethical realism) is the position that ethical sentences express propositions that refer to objective features of the world (that is, features independent of subjective opinion), some of which may be true to the extent that they report those features accurately. This makes moral realism a non-nihilist form of ethical cognitivism (which accepts that ethical sentences express propositions and can therefore be true or false) with an ontological orientation, standing in opposition to all forms of moral anti-realism[1] and moral skepticism, including ethical subjectivism (which denies that moral propositions refer to objective facts), error theory (which denies that any moral propositions are true), and non-cognitivism (which denies that moral sentences express propositions at all). Moral realism's two main subdivisions are ethical naturalism and ethical non-naturalism.[2]
I doubt many people care about metaethics, wisely so perhaps since it's plausibly the case that a person's opinions on metaethics have little bearing on their actions. Even among people who do care about metaethics, I suspect their opinions on metaethics have little bearing on their ethical beliefs, e.g. a person who identifies as a utilitarian is going to continue to identify as a utilitarian if they change their views on metaethics. And that also applies to me. I'm basically a rule utilitarian, and while I don't have strong opinions on metaethics, I strongly doubt I'll change my ground-level ethical views regardless of whatever stance I take on metaethics in the future. However, I do think that how much I live in accordance with these ground-level ethical views is dependent on my metaethical stance. Namely, is moral realism true?
While I do think it's plausibly the case that a person's opinions (or lack thereof) on metaethics would have little bearing on their actions, I'll stress that I think that only holds nowadays. In the past, one could easily argue that a person's metaethical stance did influence their actions, and that's because people in the past were more religious. There was a (strongly held) belief in God, and God provided objective moral reasons to do this or that, and people took those reasons seriously and abided by them. But I would add that this influence that metaethics (in the form of belief in God) had on our actions is hard to disentangle from the influence that our religious communities had on our actions, since we are of course social creatures and care about what other people think and tend to follow norms and practices. The thing is, fewer people strongly believe in God, so metaethical questions invariably became more abstract (not having to do with God), and I think people just don't care as much if nothing as intuitive as God has anything to do with these questions. Though again, this trend is coupled to the trend of decline in community, and especially religious communities, so it's hard to determine whether the main reason people care less about metaethics and that metaethics has less influence on people's actions (as I believe) is due to lack of belief or lack of (religious) community, but probably both have a sizeable effect (and of course, there's a reason why they're so tightly coupled). Regardless, my main point is that people's actions don't depend on their metaethical stance as much these days, and this, to a large degree, is due to a decline in religion.
I could be wrong about others and how they might change if their metaethical stance changes. In my case, however, moral realism functions similarly to a belief in God. For one, just having an objective moral reason to do something makes me more inclined to do it (otherwise, there's a nagging, nihilist voice in my head telling me that nothing really matters and morality is fake). Second, it's reassuring to know that there's some objective moral fact about the world. Even if everyone else is doing something bad (often the case in history and prehistory), I take solace in knowing that they are objectively wrong. Perhaps this also holds for other (normal) people too, but I don't know and just think it's unlikely for the reason given above (decline in religion). Anyway, my point is is that's why I care about metaethics.
To reiterate, my belief in moral realism mirrors a belief in God and especially the accompanying doubts. Though one crucial difference is that a belief in God leads to an obvious tension with the fact that the world is horrible in many ways (and so why hasn't God done anything about this problem of evil), and I don't think there's any such tension for moral realism. Still, there is still tension between moral realism and a more secular, physicalist worldview that I think that is (implicitly) common and now the default among educated Westerners. The fundamental doubt I have is that this metaethical question won't ever be resolved satisfactorily, among humans at least, and I'll probably go back and forth on it for the rest of my life.
Some caveats:
Finally, I'm curious, if anyone reading this, does the above ring true to you? I'll want to dig up some evidence for religious people being more charitable and such.
Setting these things aside, however, we can have some fun reading the arguments about the question - is moral realism true?
(Funnily enough, after writing this section, I came across an article by Lance Bush where he speculates on the adamancy that moral realists have about the repugnant nature of moral anti-realism. I will discuss later.)
Here I try to summarize in my own words a few of the arguments are for moral realism and what motivates them.
First of all, one argument against moral realism goes like this: it's clear that all the different cultures that have existed have different moral beliefs to varying degrees. Why is that the case if not for different intuitions about morality? And why would there be so many different intutions about morality if there were an objective morality out there? Furthermore, based on what we know about evolution, why would we expect our evolutionary psychology to care about morality? One might even observe that for much of human history and prehistory, our psychology disposed us to commit heinous actions, like genocide and enslavement.
How do I think about this? First of all, things have gotten "better", and there has been some moral convergence across peoples despite prevailing cultural norms. By better, I of course mean more in accordance with what I believe to be morally good, such as the abolition of slavery and (presumably, I have to check, but seems very likely) the decline in genocide. But a couple counterpoints. Even if we assume the world has gotten better with respect to these measures, to what extent are these changes due to deliberate changes in how people think about morality? I'm sure that that change has taken place to a moderate degree, but I suppose it's also the case that things like economic liberalization and technological progresss in the social realm invariably leads to more social harmony. I can't show that the causal arrow points from "social harmony" (or at least something like social distance) to declines in e.g. slavery and genocide; I'm just pointing out that there are other putative factors besides people becoming increasingly knowledgeable in (objective) morality and that it's hard to disentangle moral progress from progress in other measures (e.g. technological progress). The other point is that it's entirely plausible in my opinion that things can decline, especially among say the remnants of a nuclear war. I do think there's evidence that intelligence leads to convergence toward prosocial norms, which naively provides some evidence for moral convergence (and an objective morality), much of this convergence can be explained by prosocial norms leading to more economic growth, wealth, and productivity. In a low-trust society where gains from being prosocial are far less certain, I would expect for intelligent people to be less prosocial in that society, though perhaps more than average (and more prosocial among themselves). But again, the main issue is it's difficult to disentangle convergence in moral norms due to moral reasons or pragmatic reasons of self-interest. Still, I think it's clearly the case that as societies progressed technologically, they applied their greater ability to reason to moral questions, and came up with things like the golden rule.
Regarding the "evolutionary debunking" argument, which again is the argument that selection wouldn't favor moral reasoning (versus reproductive fitness), I think that broadly speaking, that can be construed as true insofar as much of natural selection acts on bacteria and other organisms where morality probably can't apply in any meaningful sense. Once animals are taken into account, there is a world of "badness" where morality could conceivably apply but doesn't. In other words, a predator isn't thinking about how bad it is to suffocate its prey and such. It happens to be the case that the predator evolved some behaviors that lead to a lot of suffering, however unnecessary the suffering might seem with no apparent morality. But it's also of course the case that animals live in a constant state of poverty and that these evolved and perhaps seemingly cruel behaviors are what ultimately led to reproductive success of some members. Up to now, it's fair to say in my opinion that morality plays no role in these behaviors.
But humans are clearly special as a social species that rapidly evolved a large brain. And as we evolved, we did develop rules of conduct that have some semblance to our current morality. And again, I would say that as we got smarter, our moral systems reveal some moral convergence and perhaps most importantly, reasoning applied to morality. So perhaps it's no coincidence that smart societies converge to similar moral systems.
Mike Huemer wrote about this here: https://fakenous.substack.com/p/a-liberal-realist-answer-to-debunking
Another argument for moral realism has the name "partners in crime" argument.
convergence argument
Mike Huemer has an "ontological proof" of moral realism: