People who agree about objectives can still have (non-moral) policy arguments. That may be due to a misunderstanding or a lack of knowledge by some of the parties, or simply because society (and hence the economy as part of it) is an extremely complex dynamic system that we only understand in broad strokes. That's when the good kind of economics happens. (Unfortunately, most economics that you see in public is the bad kind perpetuated by "think tanks".)
Insofar as they can be called arguments at all, they rest on moral -- or at least, "subjective value", which some would see "moral" as a subset of, with other subsets including "aesthetic" and probably some others; these distinctions are not well-defined and, ultimately, I don't think actually meaningful -- bases.
> To the extent morality can be reduced to cause-effect propositions, it can also be subject to analysis
To the extent something can be reduced to cause-effect proposition, it is a fact question, not a value question. Morality consists of the space of value questions. It may be necessary to answer a fact question to address a value question in a particular value framework, but ultimately a question that can be reduced to cause-effect propositions is not a moral question, but a fact question (which may also have utility in addressing a moral question.)
All policy arguments are moral. Economics (to the extent it is a useful, predictive, empirical science) can tell you what outcomes to expect from what actions, but not tell which actions should be preferred, without first assuming some moral values.
(OTOH, some of what passes for economics is itself not a predictive, empirical science but a form of moral advocacy in itself; but in that sense, you can't distinguish "moral" from "economic".)