Poke - "most 'moral' differences between countries, for example, are actually economic differences"

I'd state that slightly differently: not that moral differences just are economic differences (they could conceivably come apart, after all), but rather, moral progress is typically caused by economic progress (or, even more likely, they are mutually reinforcing). In other words: you can believe in the possibility of moral progress, i.e. of changes that are morally better rather than worse, without buying into any particular explanatory story about why this came to be.

(Compare: "Most 'height' differences between generations... are actually nutritional differences." The fact that we now eat better doesn't undo the fact that we are now taller than our grandparents' generation. It explains it.)