Angie Bauer and Jennifer Schreiner had been together for eight years. They had raised several adopted and foster kids. But they wanted a baby of their own. They tried a sperm bank, but their doctor, according to Bauer, refused to sign a document saying they were fit to raise a child. So they posted an ad on Craigslist.

William Marotta, a fellow foster parent, answered the ad. He and his wife exchanged emails with the couple and visited their home. He wanted to be sure that the child would be well cared for. In March 2009, he donated his sperm, waived compensation, and signed a contract renouncing parental rights and responsibilities. Schreiner carried the pregnancy. Nine months later, she and Bauer had their baby girl.

A year after the birth, in December 2010, Bauer and Schreiner split up. That’s all too common: Among women their age who have ever married, about 30 percent are divorced, and the average length of first marriages is eight years. But they stayed on good terms and continued to share parental duties.

Then their finances unraveled. A year ago, Schreiner applied for public assistance. Bauer, the breadwinner, lost her ability to work, apparently due to an ongoing illness. Schreiner, now single, filed for Medicaid to get health insurance for their daughter.

The Kansas Department of Children and Families was willing to help, but only if Schreiner cooperated in identifying the girl’s father and making him pay child support. Why should taxpayers be on the hook if the noncustodial parent could cover the girl’s expenses? Bauer tried to explain that as co-parent and breadwinner, that responsibility was hers. But the agency blew her off. Kansas doesn’t recognize gay marriages, marriage-like domestic partnerships or adoptions by same-sex couples. According to Bauer, a bureaucrat told her “he wasn’t going to discuss anything with me because I’m not the parent or legal guardian.”

Instead, the state targeted the closest thing the girl had to a male parent: the sperm donor. The agency told Schreiner she wouldn’t get any help unless she coughed up his name. So she did. And now the state is suing Marotta for nearly $6,000 in medical expenses for the child. Never mind the predonation contract in which the parties had stipulated, “Jennifer and Angie further agree to indemnify William and hold him harmless for any child support payments demanded of him by any other person or entity, public or private.” The state says that contract is meaningless, since the sperm donation wasn’t administered by a doctor. Furthermore, the state argues, under Kansas law, “a person cannot contract away his or her obligations to support their child.”

But the problem at the core of this fiasco isn’t that Kansas won’t let a noncustodial parent renounce her obligations. The problem is that when the couple is two women, Kansas won’t let that parent — in this case, Bauer — undertake those obligations. If the nine-year, multi-foster-child relationship between Bauer and Schreiner had been legally recognized, with Bauer formally named as the second parent on their daughter’s birth certificate — and perhaps if it were easier for lesbian couples to access sperm banks instead of resorting to Craigslist — the chain of parental responsibility would have been clear.

This is what makes the resistance to same-sex marriage, in Kansas and many other states, so exasperating. In family policy, conservatives are right about so many things. Children do better when they’re raised by two parents. Stability is best, and marriage promotes stability. And parents, not taxpayers, are responsible for their children. The state has every right to identify and enforce that responsibility. The best way to honor these principles isn’t to abandon or pervert them when the couple in question is gay. The best way is to apply them equally.

William Saletan covers science, technology and politics for Slate.