I've never found the moral argument for morality—except in its epistemic variety—particularly compelling. But now I find myself pulled to find plausible premises (1) and (2) of the following pretty standard argument:
- Only things that are infinitely more important than me can ultimately ground absolutely overriding rules on me.
- Rules without ultimate grounding are impossible or not absolutely overriding.
- I am a finite person.
- The only things that could be infinitely more important than a finite person are or have among them (a) infinitely many finite persons or (b) an infinite person.
- Moral rules that apply to me are absolutely overriding.
- Moral rules that apply to me are not grounded in a plurality including infinitely many finite persons.
- So, moral rules that apply to me are grounded at least in part in an infinite person.
- So, there is an infinite person.
I find (4) quite plausible. It's based on the personalist intuition that persons are the pinnacle of importance in reality. Merely Platonic entities, should there be any, while perhaps beautifully structured and infinite in their own way are not important, not unless they are persons as well.
Next, (5) is obvious to me. And (6) seems very plausible. The only plurality of finite persons who could plausibly provide a ground for the moral rules that apply to me is a human community, and there are only finitely many humans. Even if we live in an infinite universe with infinitely many people, the infinitely many aliens surely are not needed to ground the absolute wrongness of degrading a fellow human being.
All that said, I am a dubious about (1). I think there are no reasons other than moral reasons, and so the fact that moral reasons take priority over other reasons is a triviality.
But even within this controversial framework, I am now realizing there is room to ask the question of why some reasons are absolutely conclusive—they should close deliberation no matter what else has been brought to bear. "But A requires intentionally degrading my neighbor" should close deliberation about A: it doesn't matter what reasons there are for A once it becomes clear that A requires intentionally degrading my neighbor.
And that makes something like (1) still plausible. For nothing but a person can be the ultimate ground for a rule whose deliberative importance is so absolutely conclusive—nothing but a person matters enough for this task. Could this person just be my neighbor? Yes—but only if my neighbor is infinitely important, and important in a personal kind of way. This infinite importance can be had in two ways: either my neighbor is an infinite person, or else the infinite importance of my neighbor is derivative from other persons (if it's derivative say from Platonic entities it's not the right kind of importance, for only considerations about persons can bestow the kind of importance that trumps all conflicting considerations about persons). In the latter case we get a regress that is vicious unless there is an infinite person or an infinite number of finite persons grounding the rule. The latter is implausible, so there is an infinite person.
This argument requires deontology, of course.
Let me end by saying that none of this means I am being pulled to Divine Command Metaethics (DCM). DCM is just one among many ways of grounding morality in an infinite person, and it seems to me to be less plausible than other ways of doing so.