I don't agree with you that good is purely subjective.
But, in practice, what is good is highly contested, and open to philosophical and political debate. In some ways, something which is objective but very difficult to know with certainty is difficult to practically distinguish from the subjective.
If I am running an open source project, I would like to welcome contributions from people who have widely differing ideas of what the "good" is. Participation in the project should not require a general agreement on what is good, or even a general agreement on what the good is (in philosophical terms), simply an agreement on the bare minimum of shared ethics necessary for the project to successfully function.
This is a substantial claim, and requires substantial evidence. Claiming that the Good (meaning the metaethical object) is objective is also a substantial claim, but observe that it's not necessary to be a moral realist to think that things can be, for all practical purposes, bad: in an intersubjective sense, a thing is bad if everybody around you agrees that it's bad.
They can all be wrong (and they frequently are!), but I'm going to go ahead and wager that they're not wrong about civil rights, not drone-striking civilians in other countries, indefinite detention of undocumented migrants, &c &c.
To say good isn't subjective is to say there is some part of the universe at some fundamental level that defines good. That's the claim that requires evidence.
Show me the "good particle" and then we'll talk. Until then I can only rationally assume something doesn't exist until proven otherwise.
Metaethics has been in discourse on this for some time. I think most the prevalent systems do reduce down to a small set of axioms (foundationalist propose a strong form of this), or a least a set of internal consistent, self-reinforcing propositions (coherentism, which doesn't necessary presume a prepositional hierarchy).
Some of the more interesting (to me) arguments of the realists/naturalists (the justification question rather than the ontological question above), consider there to be emergent properties from the nature of interaction between agents. Basically game-theory. Presume we all were psychopaths, but intelligent self-maximizing agents and not the irrational kind. What behaviors would maximize achieving our ends? What behaviors would we need to hold others accountable to support our ends? You can take this thought experiment pretty far to get an "emergent" moral system with first-order properties similar to those we see in real societies. I find this insufficient though, you still need some base value system. Even the psychopath example presumes a set of ends for individuals like "continued survival" and so boils down to something like a form "utilitarianism."
> To say good isn't subjective is to say there is some part of the universe at some fundamental level that defines good.
Not especially: there is an abundance of immanent ethical theories that define the Good (or Right) in terms of basic things in our grasp: the number of people who go hungry, the number of people who die of preventable diseases, &c. These don't require some spooky or transcendental universal fundamental: they're about seeing people suffer in ways that we can measure, seeing that many patterns of suffering are generalizable, and taking actions to countermand that.
(There are also plenty of ethical systems that are both immanent and non-consequentialist. I follow one of them. But it's maybe beyond the point of the original comment to explain them.)
> there is an abundance of immanent ethical theories that define the Good (or Right) in terms of basic things in our grasp
The problem with all those theories, is they can be attacked as simply efforts to define "good" – with the ensuing problem that other people will define "good" in contrary ways, and if "good" is just a definition, then how can a mere definition be, in an objective sense, superior to a competing proposed definition?
That's basically G. E. Moore's argument against naturalistic objective ethics. If one agrees with it, then the only options available are to reject objective ethics, or to reject naturalism.
Fair enough! I wasn't expecting to have Moore's naturalistic fallacy pulled on me :-)
Neither intersubjective nor Kantian ethics have this problem: intersubjective ethics doesn't admit of an objective Good, and Kantian ethics don't admit of an is-ought distinction (all "ought"s are in fact "is"es that are bound in actions).
> intersubjective ethics doesn't admit of an objective Good
I agree, but intersubjective ethics might not actually work in practice in a world in which people are approaching ethics from wildly different starting points. Consider an issue like abortion – people who support the legal availability of abortion, and people who oppose it, have such widely different ethical views that I think there is no intersubjectivity to be had (on that issue at least)
> Kantian ethics don't admit of an is-ought distinction (all "ought"s are in fact "is"es that are bound in actions).
I wonder, if you could expand on that point?
In my mind, Kant's categorical imperative could be viewed as either a proposed definition of the good (in which case Moore's argument is applicable), or a claim about what actually is good (in which case it escape's Moore's argument)
> In my mind, Kant's categorical imperative could be viewed as either a proposed definition of the good (in which case Moore's argument is applicable), or a claim about what actually is good (in which case it escape's Moore's argument)
It’s an academic opinion, but I believe it’s the latter: the very first line in the GMS asserts that the metaethical object itself is the good will: “nothing in the world (or indeed beyond it) can possibly be conceived as good without qualification except for the Good Will.”
The CI is the logical consequence (according to Kant) of what the good is. But that distinction is definitely subtle in the context of his normative ethics.
All those still depend on the idea that humans and life itself are more than just a long running, self-replicating electrochemical reaction which again pushes the burden of proof on to you.
Going back to the original response: you don't actually need to be a moral realist to observe (as in, witness with the globs of goo in your eyesockets) intersubjective ethics.
You don't have to agree with them, but it's a real phenomenon. It's up to you to decide how you handle it.
You are assuming naturalism / physicalism / materialism is true.
I agree, that if naturalism / physicalism / materialism is true, then the concept of "objective good" becomes hard to justify. Certainly, some people have tried, but a lot of people question whether those attempts can be successful – indeed, doubting those efforts is one thing that both naturalists who doubt the objectivity of the good, and non-naturalists who believe in the objectivity of the good but reject the idea that it can be given a naturalist foundation, can agree on.
