In your interpretation, Hubbard's framework is a liberal feminist one (important as it is), similar to J.S. Mill's. I'm not sure if your interpretation is a valid one, but I agree that Hubbard's point of view is not the same as Thomas Laqueur's. Liberal feminists, by and large, accept reproduction as the biological determinant of sex and leave it at that, but even they have an objection to the double standard inherent in having one half of humanity classed as "the sex" (as they used to say) while the other half is left as the paradigmatic "person" in the "social contract": "No one has suggested that men are just walking testicles, but again and again women have been looked on as though they were walking ovaries and wombs" (Ruth Hubbard). The limit of Hubbard's criticism is the limit of liberal political theory, which may be best characterized by Rousseau's remark on sex: "The male is only a male now and again, the female is always a female...; everything reminds her of her sex" (_Emile_). We Marxists are interested in going beyond a dialectical couple of liberalism and its discontents, no? For this purpose, sex, too, must be understood as a political interpretation of biological facts.