I’m a normative antirealist but I don’t think non-naturalist normative realism is intelligible. As such, I find many of the considerations that assign nonzero credence to it hard to fathom. I don’t know how to assign credence to utterances that I don’t think are propositions and if they are I don’t know what those propositions are.
I don’t think it makes any sense to talk about things “mattering” in a stance independent way. It sounds like saying something can be strance independently fun or intrinsically tasty. Things matter to me. But I don’t think the things that matter to me themselves have “matterworthiness.”
Also, since I only act based on what matters to me, as far as I can tell it wouldn’t matter to me whether anything mattered in the sense that realists seem to think that things matter. In other words, their very concept of the way in which things matter doesn’t matter to me. Think about trying to have a tasty meal. I am going to eat foods that taste good to me, not foods that are “objectively tasty” independent of how they taste to me. Likewise, even if there were objective normative facts, well, so what? Why care about them?
I don’t know if I count as a nihilist, as it’s unclear what precisely is meant by the term in this and other contexts. I don’t think there are stance-independent normative facts, and I don’t think anything “matters” independently of it mattering to people, but I find it strange to suggest that if nothing matters in the former sense that nothing matters in the latter sense.
Compare all this to gastronomic realism and nihilism. A gastronomic realist may claim there are facts about what food is intrinsically tasty or not tasty that is true of that food independent of how it tastes to anyone. A gastronomic nihilist would deny food is tasty or not tasty in this way. Food itself, they might maintain, is neither tasty or not tasty independently of how it tastes to people. But that doesn’t mean people can’t find things tasty or untasty. It just means that to find something tasty is to have a particular kind of psychological attitude towards it. Just the same, one could have moral attitudes, or stances, towards some actions and not others. And things can matter to someone. But I have no idea what it would mean for an action to be right or wrong, or for a particular set of considerations to “matter,” independent of anyone’s stances, or how much they matter to people. I think things can matter to people, but they can’t just matter simpliciter.
In that sense, I take a much stronger stance towards non-naturalist normative or moral realism than what seems implied in the post here: I am not convinced non-naturalist normative realism is even a meaningful position to take. As such, it’s unclear to me how anyone could assign credence to it being true, since it’s not clear to me it’s the sort of thing that could true or false in principle, for the same reason a string of meaningless words couldn’t be true or false. One way to put this is that I don’t think normative realism’s problems are metaphysical so much as conceptual.