Sexuality is to feminism what work is to marxism: that which is most one's own, yet most taken away. Marxist theory argues that society is fundamentally constructed of the relations people form as they do and make things needed to survive humanly. Work is the social process of shaping and transforming the material and social worlds, creating people as social beings as they create value. It is that activity by which people become who they are. Class is its structure, production its consequence, capital a congealed form, and control its issue.
Implicit in feminist theory is a parallel argument: the molding, direction, and expression of sexuality organizes society into two sexes - women and men - which division underlies the totality of social relations. Sexuality is that social process which creates, organizes, expresses, and directs desire, creating the social beings we know as women and men, as their relations create society. As work is to marxism, sexuality to feminism is socially constructed yet constructing, universal as activity yet historically specific, jointly comprised of matter and mind. As the organized expropriation of the work of some for the benefit of others defines a class - workers - the organized expropriation of the sexuality of some for the use of others defines the sex, woman. Heterosexuality is its social structure, gender and family its congealed forms, sex roles its qualities generalized to social persona, reproduction a consequence, and control its issue.
Marxism and feminism are theories of power and its distribution: inequality. They provide accounts of how social arrangements of patterned disparity can be internally rational yet unjust. But their specificity is not incidental. In marxism to be deprived of one's work, in feminism of one's sexuality, defines each one's conception of lack of power per se. They do not mean to exist side by side to insure that two separate spheres of social life are not overlooked, the interests of two groups are not obscured, or the contributions of two sets of variables are not ignored. They exist to argue, respectively, that the relations in which many work and few gain, in which some fuck and others get fucked, are the prime moments of politics.
Catharine MacKinnon, "Feminism, Marxism, Method, and the State: An Agenda for Theory", in N. O. Keohan et al. (eds.), Feminist Theory: A Critique of Ideology, 1982