Veganism

[Paleophyte]

It doesn't predict agreement because people can disagree for reasons unrelated to any given proposition being true or false, as mentioned, but it does suggest things like a/any rational moral agent a, supplied with facts b, could/must conclude c.  Ethicists might lean on concepts like perfectly rational agents when trying to describe basic system principles, despite there being no such example of such a thing in the human race, to point out the disparities in what we might rationally conclude compared to what we actually do.  People can be ignorant of facts, and it's not hard to see how not knowing something about a thing might lead to a different of conclusions about that thing if you were aware of that fact.  This is why vegan/vegetarian ethics often takes time to explain to people facts about animals that they may not, or many people do not, know.  Facts that seem to inform other moral conclusions we accept as true - making it an issue of consistency if nothing else.  That's the very question the op lead with.  What disparity in fact between animals and people makes it (seem) okay to eat animals, but not people?  Or would, if it's okay to eat animals even in light of those facts, somehow still not make it okay to eat people to whom those same facts apply.  

I'd probably agree that realism isn't the most practical system.  You have to think about shit.  You have to know shit.  It matters whether or not you have the facts correct.  You can be wrong.  Emotively, if we didn't know how we felt about something or had never thought of it before revulsion in the doing of it (or joy) is immediately instructive.  Subjectively, we do tend to know what we think about a thing, or can quickly arrive at a basic opinion.  Deontologically, we're good at lists and lists are succinct and practical.  Realism's real benefit is in accuracy.  Either accuracy in description of fact or accuracy of communication.  Realism says, for example, if what you mean when you say a thing is ad is a thing is yuck..then say yuck, because the thing being "bad" isn't really true.  Not as the reason for your opinion and not as the thing you're actually experiencing.  If you have an opinion on a thing, and it's not based in objective facts about that thing..then just communicate it directly as the opinion not based in fact that it is.  If, however, you think that there actually is something bad about assault, or actually is something good about helping people...that it's not just yummy to you or an opinion you cannot support with objective facts about assault and helping people...that's realism.

As far as evidence for moral truth as a phenomena, it's actually pretty strong.  From core principles of moral systems that are shared between individuals and cultures through time that allow us to recognize them -as- moral systems and even specific types of moral systems, to the neurology of moral consideration - where we see that we're genuinely trying to use the regions of our brain that deal in what we otherwise call fact (not exclusively! - there are neurological explanations for what realists might call emotivist, subjective, or relativistic moral failure), to the contents of the specific realist statements themselves.  If I wanted to explain why I think assault is bad I would inevitably talk about the physical and mental effects of assault on both parties, the historic consequences of permissive violence, though I may also just point at a victim and say "you look at that and figure it out yourself".  Think about it.  You probably wouldn't want to be quoted under a picture of some vicious domestic abuse saying "there's no evidence or fact that suggests doing this to a person is wrong".

I have no problem with morality based on reality. It's pretty obvious what happens if you have a society of rapey murder thieves. That's just an underlying reality and we can model it with some pretty simple math. We've got negative-sum games figured out. I just don't see the need to invoke 'moral truths' to explain these underlying physical principles. That smacks of mysticism that does nothing but obfuscate to me.

[Disagreeable]

It seems like you’re treating disagreement as evidence against realism but not treating agreement as evidence in the other direction. What’s the principled basis for that asymmetry?

The one where you've failed to demonstrate agreement. What part of that confuses you?

But you're saying that if people agree on moral matters it's not real agreement, it's just what's fashionable or it's a fluke 'it's just a lucky shot' to use your analogy.

But what is your justification for it just being a lucky shot, and not being real agreement?

You're acting like this is obvious but you're still begging the question. What's in question is precisely: why can't we have real agreement that is evidence in favor of realism if we can have disagreement that counts in favor of anti realism? What is your argument for agreement not being real agreement?

To put it another way, why should we prefer your analogy over the analogy of somebody who is initially a very bad shot when it comes to shooting an arrow at a target, but with lots of practice becomes a better shot, despite perhaps still being a bad shot, and hits the target more often due to improved skill rather than just lucky shots (so there is more agreement later on, moral progress)?

[Disagreeable]

It demonstrates that there is no evidence for these 'moral truths' that you're babbling about. This has been my point from the beginning.

You're not actually demonstrating that there is any more evidence for anti realism than for realism. You're just discounting any moral agreement as just what's fashionable or just a fluke, without giving a reason, which just begs the question against anti realism. Your 'argument' or 'evidence' just assumes what's in question.

If realism doesn't predict agreement, then it predicts pretty useless 'moral truths'.

Just because people don't agree on what's moral doesn't mean that there isn't a fact of the matter about what's moral, nor does it mean that what's moral doesn't matter.

[Fake Messiah]

To put it another way, why should we prefer your analogy over the analogy of somebody who is initially a very bad shot when it comes to shooting an arrow at a target, but with lots of practice becomes a better shot, despite perhaps still being a bad shot, and hits the target more often due to improved skill rather than just lucky shots (so there is more agreement later on, moral progress)?

It is a false analogy. In your archery analogy, the target exists in physical space. Both the archer and the spectators can see it, touch it, and agree on where the bullseye is located. In morality, there is no "visible" target. Unlike a physical object, we cannot point to a "Moral Fact" in the natural world.

When an archer misses, they know they missed because the arrow is in the dirt. When societies disagree on morality (e.g., the ethics of euthanasia or wealth distribution), there is often no consensus on who "missed" and who "hit."

If morality were as objective as target practice, we would expect to see a convergence of belief over time as "skill" increases. So, moral "progress" is actually just moral change—a shift in cultural sensibilities rather than a closer approximation of a pre-existing truth.

[Nay_Sayer]

Animal Holocaust sounds like the name of a punk band that only plays in dive bars right after the Phish cover band.

[The Grand Nudger]

I have no problem with morality based on reality. It's pretty obvious what happens if you have a society of rapey murder thieves. That's just an underlying reality and we can model it with some pretty simple math. We've got negative-sum games figured out. I just don't see the need to invoke 'moral truths' to explain these underlying physical principles. That smacks of mysticism that does nothing but obfuscate to me.

We might also say that it's pretty obvious what happens when you bring a semi-domesticated mammalian terrorist into your home and we don't need to invoke "cat truths" to explain that.  

I don't see much mysticism in a broken face.  I do see moral concern.  I'm certainly aware that people with mystical values systems see the value of moral realism and, wishing to possess it for their mystical beliefs, and often their mystical beliefs exclusively, have done alot of harm to the label.  If the best explanation for a things goodness or badness that a person can dream up is some ghost - they may use the label of moral realism - but they strongly disagree with the content of it - which, imo, is what matters.

-and matters specifically because it is accurate, as opposed to obfuscatory.

[The Grand Nudger]

It is a false analogy. In your archery analogy, the target exists in physical space. 

In moral realism, so do the objects of moral truth.  This is exactly what it means to say that a thing or statement or proposition or claim is metaethically objective.  

So if I say something like.... females don't have the mental ability to make their own decisions, so males must shoulder the responsibility of making decisions for them...I'd better be ready to show their lack of mental ability as a target in physical space..at a minimum.  I think most people here would agree that notion has been thoroughly debunked in every possible way.  Logically, in principal.  Scientifically, through research.  Demonstrably, through standardized testing.  Practically, by all these females making decisions all day irl. I don't think that's just someone's tastes, or just their opinion - I think it is a failed attempt at a statement of fact. Even if we assumed we do have the responsibility of making decisions for them...because I do think there are classes of people this statement is accurate about.....it wouldn't be because they were our mental lessers, as it claims to premise this responsibility on.