The Party is wary of anything they cannot control, so it naturally attempts to undermine such institutions as marriage and the family, and to remove the pleasure and joy of amorous relations. On family, the Party encourages children to sell out their own parents for expressing unacceptable ideas:
...hardly a week passed in which ‘The Times’ did not carry a paragraph describing how some eavesdropping little sneak —‘child hero’ was the phrase generally used — had overheard some compromising remark and denounced its parents to the Thought Police.
Similarly, the Party attempts to remove love and especially eroticism from sex. The sex act was to be undertaken only with the purpose of creating children to serve the Party. While the Party did not exacly oppose occasional relations with the proles, they wanted such relations to be stripped of romance:
The aim of the Party was not merely to prevent men and women from forming loyalties which it might not be able to control. Its real, undeclared purpose was to remove all pleasure from the sexual act....Sexual intercourse was to be looked on as a slightly disgusting minor operation, like having an enema.
Sexual activity and temptation seem to be associated with women. Though Orwell does not explore the point, it is women who join the ranks of the Anti-sex League, and it is Julia who approaches Winston to begin their relationship. Overall, though, it is not so much sexism but the desire to control every possible aspect of the human condition that motivates the Party.