Many posts here strongly dismiss [moral realism and simplicity], effectively allocating near-zero probability to them. I want to point out that this is a case of non-experts being very much at odds with expert opinion and being clearly overconfident. [...] For non-experts, I really can't see how one could even get to 50% confidence in anti-realism, much less the kind of 98% confidence that is typically expressed here.

One person's modus ponens is another's modus tollens. You say that professional philosophers' disagreement implies that antirealists shouldn't be so confident, but my confidence in antirealism is such that I am instead forced to downgrade my confidence in professional philosophers. I defer to experts in mathematics and science, where I can at least understand something of what it means for a mathematical or scientific claim to be true. But on my current understanding of the world, moral realism just comes out as nonsense. I know what it means for a computation to yield this-and-such a result, or for a moral claim to be true with respect to such-and-these moral premises that might be held by some agent. But what does it mean for a moral claim to be simply true, full stop? What experiment could you perform to tell, even in principle? If the world looks exactly the same whether murder is intrinsically right or intrinsically wrong, what am I supposed to do besides say that there simply is no fact of the matter, and proceed with my life just as before?

I realize how arrogant it must seem for young, uncredentialled (not even a Bachelor's!) me to conclude that brilliant professional philosophers who have devoted their entire lives to studying this topic are simply confused. But, disturbing as it may be to say ... that's how it really looks.