I would characterise antirealism as something like 'believing that there is no normative space, and hence no logical or empirical line of reasoning you could give to change someone's motivations.'

I would not accept this characterization. Antirealism is the view that there are no stance-independent moral facts. I don’t think it logically entails any particular normative implications at all, so I do not think it has no “normative space” or “no logical or empirical line of reasoning” you could give to change someone’s motivations. 

I would be interested to hear a counterexample that isn't a language game. I don't see how one can sincerely advocate someone else hold a position they think is logically indefensible.

I’m not sure what you have in mind by a language game, but you gave this as an example of something an antirealist has no access to: “Show me that their policies are more aligned with a moral view that we both in fact share.”

Why wouldn’t an antirealist have access to this? There’s a few obvious counterexamples to this. Here’s one: cultural relativism. If two people are cultural relativists and are members of the same culture, one of them could readily convince the other that a policy is more in line with the moral standards of the culture than some other policy. The same generalizes to other antirealist positions, such as various constructivist views.

Someone who believed in a moral realist view that valued a state whose realisation they would never experience - black ties at their own funeral, for instance - should be highly sceptical of a moral antirealist who claimed to value the same state even though they also wouldn't experience it.

Why should they be skeptical? I am a moral antirealist and I have all kinds of preferences that are totally unrelated to my own experiences. I want my daughter to go on to live a happy life long after I am dead, and I would actively sacrifice my own welfare to ensure this would be the case even if I’d never experience it. I don’t believe I do this because I’d feel happy knowing the sacrifice was made; I’d do it because I value more than just my own experiences.

I see no legitimate reason for realists to be skeptical of antirealists who have values like this. There is nothing special about valuing experiences I’d realize that prioritizes them over ones I won’t. 

To an antirealist it can only mean something like 'pleasing to imagine'.

That isn’t what that means to me, so I do not think this is correct. If you think this is some kind of logical entailment of moral antirealism, I’d be interested in seeing an attempt at showing a contradiction were an antirealist to think otherwise, or some other means of demonstrating that this follows from antirealism.

But if they won't be at the funeral, they won't know whether the state was realised, and so they can get their pleasure just imagining it happen - it doesn't otherwise matter to them whether it does.

When performing an action, my goal is to achieve the desired outcome. I don’t have to experience the outcome to be motivated to perform the action. 

Not by coincidence I think, this arguably gives the antirealist access to a basically hedonistic quasi-morality in practice (though no recourse to defend it), but not to any common alternative.

I don’t endorse this view, and I deny as an antirealist I’d have any need to “defend” a moral standard. This to me sounds a bit like suggesting I’d be unable to defend what my favorite color is; which is true, I just don’t think my color preferences require any sort of defense.

If you start with the common belief that there is such some 'objective' morality and some set of steps of reasoning tools that would let us access it, you can potentially correct the other's use of those tools in good faith. If one of you doesn't actually believe that process is even possible, it would be disingenuous to suppose there's something even to correct.

This still may or may not be connected to anyone’s motivations. I don’t care at all what the moral facts are. I only act based on my own preferences, and I have absolutely no desire whatsoever to do whatever is stance-independently moral.

***

I’d be happy to talk about the other claims in the sidebar as well but I’m not sure I understand some of them. Can you elaborate on these?

The uniquely non-evolutionarily explicability of utilitarianism (h.t. Joshua Greene's argument in Moral Tribes) and how antirealists can explain this

The convergence of moral philosophers towards three heavily overlapping moral philosophies - given the infinite possible moral philosophies and how antirealists can explain this

What is it antirealists are supposed to explain, specifically?

Also, I don’t intend to be argumentative about literally everything, but some of us may find other aspects of these topics more interesting than you, so which of these topics is most interesting can vary.

Why wouldn’t 6 be available to an antirealist? If I’m a utilitarian and they’re a utilitarian, I could convince them a course of action would maximize utility. This would be a bit like (1): convincing them that a course of action would be consistent with their values.

If by (7) what you mean by “correct” is demonstrating that a course of action is in line with the stance-independent moral facts, an antirealist couldn’t sincerely attempt to do that, but I don’t think this carries any significant practical implications.

And without those, the only honest/nonviolent option you have to persuade me is not going to be available to you the majority of the time, since usually I'm going to be better informed than you about what things are in fact good for me.

I don’t think I need to have better access to someone’s values to make a compelling case. For instance, suppose I’m running a store and someone breaks in with a gun and demands I empty the cash register. I don’t have to know what their values are better than they do to point out that they are on lots of security cameras, or that the police are on their way, and so on. It isn’t that hard to appeal to people’s values when convincing them. We do this all the time.

And, for what it’s worth, I think that in practice the vast majority of the time (in fact, personally, I suspect virtually all the time except for rare cases of weird philosophers) what people are doing is appealing to a person’s own values, not attempting to convince them that their values are misaligned with the stance independent moral facts.

Part of the reason for this is that I don’t think most people are moral realists, so it wouldn’t make sense for them to argue on behalf of moral realism or to appeal to others under the presumption that they are moral realists. 

Another reason I think this is because I don’t think the move from convincing someone what the stance-independent moral facts are to them acting in any particular way is that straightforward. You’d have to make a separate case for motivational internalism to show that convincing them is enough to motivate them, while if you instead abandon this, it’s possible the people you’re convincing can be persuaded of what the stance-independent moral facts are, but simply not care.

Speaking for myself, arguing for moral realism would have absolutely no impact on me. I don’t simply reject moral realism. I also deny that if there were stance-independent moral facts, that I’d have any motivation to comply with them (of course, I could be wrong about that). If I’m right, and if I have accurately introspected on my own values, then merely knowing something is stance-independently wrong wouldn’t change what I do at all. I simply don’t care if something is stance-independently moral or immoral. So why would persuading me of that matter?

Whether or not antirealists must rely, in practice, any more so on threats or manipulation than moral realists is an open empirical question. I predict that they don’t. If I had to make predictions, I’d instead predict that moral realists are more likely to threaten or manipulate people to comply with whatever they take the stance-independent moral facts to be. That at least strikes me as a viable alternative hypothesis. Either way, this is an empirical question, and I don’t know of any evidence that antirealists are in a worse position than realists. As an aside: even if they were, that wouldn’t be a good reason to reject the truth of moral antirealism. Reality may simply not include stance-independent moral facts. Even if that foreclosed one mode of persuasion, well, too bad! That’s how reality is.

As an aside, I think this remark:

This isn't to say that moral antirealists necessarily will manipulate/threaten etc - I know many antirealists who seem like 'good' people who would find manipulating other people for personal gain grossly unpleasant. 

…carries the pragmatic implication that antirealists are more likely to be immoral people that threaten or manipulate others. Do you agree?

This isn't supposed to be a substantial argument for moral realism, but I think it's an argument against antirealism.

What exactly is the argument against antirealism? Antirealists cannot honestly appeal to stance-independent moral facts when persuading others. I agree with that. But I don’t know why that should be taken as an argument against moral antirealism.

As an antirealist it would nonetheless be far better for you to live in a world where the 6th and 7th options were possible.

Well, I think the 6th collapses into the first and that the 7th has no practical benefits, so I’m not persuaded this is true. I do not think we’d be better off in any way at all if moral realism is true, and I am not convinced you’ve shown that we would be.

More generally, I simply deny anything about antirealism leaves in an especially weak position to rely on threats or manipulation. Antirealists can appeal to people’s values. And I think moral realists would have to do exactly the same thing. If the person in question doesn’t care about what’s true or isn’t motivated by what’s moral, then the realist is going to be in the exact same boat as the antirealist. The only thing the realist does is saddle themselves with more steps.

I don't think I defended my remarks on the matter as well as I could have, and David Moss has brought to light some of what Bentham initially said and used that to make a good point. MichaelDickens, you've expressed a critical stance towards the post I wrote that uses the term "quackery" and is polemical. 

But if you take a look, you will see from the tone and links provided that I am responding in an ongoing exchange that has spanned quite some time. During that time, Bentham has routinely made far more inflammatory and insulting remarks about antirealist views. For instance, this was a section heading he used in an early post on moral realism (one of the two I linked a response to here):

Cultural Relativism: Crazy, Illogical, and Accepted by no One Except Philosophically Illiterate Gender Studies Majors

You can find this here.

Bentham also repeatedly describes views like mine as "crazy". Here's one example:

Well, in this article, I’ll explain why moral anti-realism is so implausible — while one always can accept the anti-realist conclusion, it’s always possible to bite the bullet on crazy conclusions. Yet moral anti-realism, much like anti-realism about the external world, is wildly implausible in what it says about the world.

I worry that you drew a conclusion about my tone without taking into consideration Bentham's own tone and what I was responding to.

 In fact, it seems to me and many (most?) people that underserved pain (in the aforementioned sense) is bad regardless of what attitudes other people have about such pain. 

I'm a moral antirealist, and I myself think that undeserved pain is bad regardless of what attitudes other people have about such pain. The reason I think such pain is bad is because I disapprove of it. So what you've described is completely consistent with antirealism. For comparison, I think pineapple on pizza tastes good regardless of what other people have about it.

What would be required for a person's stance about this scenario to suggest realism is if they thought that pain was bad regardless of what anyone thought about it, including themselves and the person experiencing the pain. That is, they'd need to think that the pain would be bad even if they didn't think it was bad and even if the person experiencing the pain didn't think it was bad. And I don't think most people think this.

I'm familiar with phenomenal conservatism (I've directly discussed moral realism with one of its main proponents, Mike Huemer here, and have written a bit about the topic such as here). I don't endorse it, but even if I did, I think its frequently misused and isn't going to do much to support realism. At best, phenomenal conservatism provides one with a private, extra source of "justification" for one's beliefs, but it has little dialectical force in an argument. The fact that something seems a certain way to you may matter to me a little bit to me, but if it doesn't seem that way to me (or it seems that the contrary is the case), how things seem to you won't count for much.

My grounds for this are the relatively-basic ones: it certainly seems, for example, that some choices are plain irrational or that some states-of-affairs are bad in a stance-independent way

Seems that way to who? It does not seem that way to me. If I had to say how things "seemed," I'd say it seems to me that this is not the case.

And of course, robust realists will always point to the partners-in-crime of moral facts, in other kinds of a priori domains. 

They do, but I don't find these arguments even a little convincing. I don't see any good reasons to be a normative realist in any nonmoral domains, either.

Personally, I think there are very serious problems with people relying so heavily on how much things seem to them. Among other issues, I don't think there are good ways to resolve conflicts if things seem differently to others.

I think pain is bad, but I don't think pain is bad independently of what I or anyone thinks about it. I think pain is bad insofar as I don't like being in pain and don't want anyone else to be in pain (all else being equal). Why be a realist about the badness of pain, or anything else? While I agree arguments for moral antirealism are typically not very good, I also do not think there are any good arguments for moral realism, nor any particularly good reason to think moral realism is true.

You also say the view should be taken very seriously. Why should it be taken very seriously?

You suggest antirealism has undesirable properties, then say:

But moral antirealism is ultimately a doctrine of conflict - if reason has no place in motivational discussion, then all that's left for me to get my way from you is threats, emotional manipulation, misinformation and, if need be, actual violence. Any antirealist who denies this as the implication of their position is kidding themselves (or deliberately supplying misinformation). 

I am a moral antirealist. I don’t think I endorse a position that is a “doctrine of conflict.” However, it’s hard to assess why you think this. You suggest that antirealism entails that “reason has no place in motivational discussion.” I’m not quite sure what you mean by this, but I don’t think reason has no place. Why would I think that? Perhaps you are thinking of “reason” differently than I am? If you could elaborate on what you are claiming here, and how you are thinking of some of these notions, that would be helpful.

As an antirealist, I don’t rely on threats or emotional manipulation or misinformation any more than anyone else, and I don’t know why I would if I were an antirealist. I don’t think antirealism has anything to do with having to rely any more on any of these than moral realism does. Why would it?

Why do you find emotivism convincing?

Why would phenomenal conservatism imply some form of moral realism?

What is the reason not to eat the car that isn’t grounded in concern for wellbeing or some other value the person already holds?

 Realists might just say you have a reason simpliciter. There's nothing more to it than that. And they think this because it's intuitive.