A moral argument for theism

1. (Premise) Humans have intrinsic goods that do not reduce to pleasure.
2. (Premise) If there are intrinsic proper functions in humans, probably God exists.
3. (Premise) If there are no intrinsic proper functions in humans, either humans have no intrinsic goods or all intrinsic human goods reduce to pleasure.
4. Therefore, probably God exists.

The first premise is the least controversial, but it, too, is controversial. Premise 2 requires a subsidiary argument. If God doesn't exist, then our only hope for an explanation of intrinsic proper functions in humans is evolutionary accounts of proper function. But evolutionary accounts of proper function all fail (see, for instance, this argument). Premise 3 is, I think, fairly plausible—except perhaps for pleasure and goods reducible to pleasure, any intrinsic human goods we can imagine (e.g., friendship, wisdom, etc.) are only good on the assumption that there is such a thing as the intrinsic proper function in a human. A lot more needs to be said about each premise, of course.

Notice that unlike other moral arguments for theism, this one does not necessarily lead to a divine command ethics. The analogue to divine command ethics would be a "designer's purpose" view of proper function. But I think that doesn't give intrinsic proper function.