Ethics can still be valuable if you're a moral anti-realist

I had a conversation at a party a few days ago. I was talking about ethics to a guy. He told me he thought ethics was pointless because there’s no objective moral reality. I told him that this didn’t follow. Here’s why.

First, methodology. How does ethics work? In a physical science you have an objective external world. You have a bunch of observations about that world. You make up rules. You test those rules against reality. Would a world that followed rule X generate the kinds of observations you have? What about new observations? Etc… Of course there’s more complexity here. We assume an ordered universe (if in the past water flows downhill, it will continue to do so). We assume that there’s a common external reality that produces our observations and that we all have access to it. We assume that more complex rules are on average less accurate and select against them etc…

When it comes to ethics, we don’t have physical observations or experiments. You can’t look at a bullet flying into a human skull and see on the atoms whether the bullet is a just one fired in self defence or an unjust one killing a mugging victim. Instead what you do have are a set of case by case moral intuitions. Eating a baby for fun. Probably bad. Stopping a murder. Probably good. You then experiment with various moral rules that fit these intuitions. e.g: Utilitarianism. You then explore various edge cases and situations where your moral rule conflicts with your moral intuition. As you do this a few things happen

• You start to notice which moral rules have predictive power and which do not
• You start to notice when and at what ration you trade off different moral preferences against each other
• You start to notice a much broader and richer set of preferences and intuitions you have, and in doing so may realize that some of your intuitions conflict with others or that certain intense moral feelings you had are not in fact based on your true, deep moral preferences but are rather surface level reactions instilled in you by external forces. None of these are dependent on there being an objective external moral reality. Even if morals are just a specific kind of preference, understanding that preference and your own utility function is useful

That being said, there is some more complexity here. Why have moral rules at all? Why not just rely on your case by case intuitions. After all, isn’t even a really good moral rule still a less accurate match for your moral preferences then “Do what I my intuition says is right in any given situation”? I’m not sure about this. For a moral realist there are simple answers. Maybe. Moral reality exists, determining it can be tricky, your initial thoughts may be mistaken/confused. Just like a mirage can appear real, so an intuition can seem real but actually reflect bias, emotion, etc… (I don’t buy this even for realists, but let’s not get sidetracked). For an anti-realist I guess my only thought is that my moral preferences, just like my non moral preferences, are not all equal and it’s only with sustained reflection that I can understand which things I value more and why. Also, disentangling which preferences you consider part of yourself and which you don’t and which ones are instrumental and which aren’t is tricky.