"Ironically, I'm making a blatant moral appeal here ("human misery is bad"), but I consider even this banal moral position a product of the social relations in which I'm embedded; it's not a universal standard by which to judge all societies."
Yes, indeed. From your standpoint it is impossible to pass judgement on anything, and yet you do, incessantly. You say "ethnocentrism" meaning something bad, which is a value judgement. In fact your moral outlook is that perfect distillation of contemporary capitalism - "Whatever" - with its origins in the End of Ideology thesis advanced by Cold War liberals like Daniel Bell and Clifford Geertz carefully tucked away out of sight.