Assume the following evo-psych explanation of sexual dynamics: women are concerned with maximizing the resources available to their offspring; men are concerned with maximizing their number of sexual partners while minimizing the resources invested in each partner.

Proposal:

Women who want children pool their resources with other women, who share childcare and housework duties more equitably than in a male/female pairing. Men have no financial or emotional responsibility for any women or children. They are free to engage in sexual or romantic relationships with women, but they are no longer included in the structure of the family. Families are structured around groups of working and non-working cohabiting women, rather than one breadwinning man and one childbearing woman. (Essentially abolishing traditional marriage.)

In this arrangement, women with children gain the benefit of a multiple-income household, while men are absolved of any obligation to provide for their romantic partners or their biological children. Add in legal, accessible prostitution and birth control (including abortion), and the traditional sexual marketplace has been destroyed. Sex is no longer associated with unwanted commitments for either men or women. Are we all happy?

Edited to ask: Some of you have raised objections to male children being raised without a male caregiver. I have a few questions. 1) Does this objection apply also for female children? 2) This proposal is not too far off from how many people live today, as other commenters have pointed out. For example, currently the majority of childcare IS done by women. This is not a hypothetical. So is the current state of affairs, with few male caregivers, harmful to children?

Second edit: For those of you linking to studies about outcomes for children in single-parent households, please keep in mind that I am not advocating single-parent or single-income households. I am advocating households with multiple earners and caregivers, with or without the presence of the biological father. If you know of any studies which compare outcomes for children in dual-income households with varying parental arrangements (one mom, one dad; two dads or moms; two co-parents who aren't romantic partners... etc), that would probably be more relevant.