Sex matters because having a certain kind of genitals at birth is a prerequisite to socialization as a “boy.” Sex matters because the social role “boy” is a more favorable social role than that of “girl.” Girls are devalued, sexualized, and discriminated against simply because they are “girls.” There are objectively measurable material advantages to being male at birth. For example, boy-socialized people will be paid more for the same work.
This is no accident; it is precisely how the human system of sex-based gender socialization works and has worked for thousands of years. Gender disproportionately distributes power to males via the cultural hegemony of over-valued masculinity. Gendered socialization begins at birth and has lifelong formative effects on the psyches of both men and women. The ugly result is institutionalized male dominance over females and femininity. There is no nation in the world primarily controlled by girl-socialized people. Not a single one. Every measurable imbalance of social power between men and women can be traced back to the false naturalization of gender roles and gender role socialization.
It doesn’t make sense, then, for us to consider male-socialized people who identify as “women” to be the same as female-socialized people who were tracked to become “women” from birth. We must have a more nuanced understanding of the social dynamics and determinants of class-based oppression.