How much does money matter when thinking about same-sex marriage, or about marriage at all? The essence of the debate—and certainly its emotional heart—lies with words like family and respect, honor and honesty, and, above all, love. But those words, and even more so others—security, protection, sickness and health, home and career—are not divorced from finances. This is particularly true when any one of them is used in the same sentence as “children.” Another number to add to the equation: eleven hundred and thirty-eight, which is the number of federal laws that rely on a definition of marriage. Many more of them are about money, in one way or the other, than about love. Nor is the concern simply that of the family involved: companies have an interest, too, as does the larger business world, in not having families live in what might be called an economic closet.

That there is a business case for marriage equality was confirmed this week with the news that at least sixty major corporations will file an amicus curiae brief in support of overturning Prop. 8—a move, depending on how the Court writes the decision, that could establish a right to same-sex marriage not only in California but in the country as a whole. (Some leading Republicans are also submitting a brief.) More may sign on before the filing deadline on Thursday. The companies range from Apple to Xerox, with everyone from Levi Strauss, Cisco, Morgan Stanley, Nike, and Panasonic in between. Fortune got a draft of the brief, which reads in part

If one believes that protecting children is a priority, then so is same-sex marriage. A third of lesbian couples and a fifth of gay couples who live together already have children, according to the Census, and a lack of access to marriage takes both social and economic security away from them. A widow or widower with a minor child whose income falls below a certain level can get social-security benefits based on the deceased spouse’s earnings—but not if the spouse is of the same sex. The same is true of tax laws, like the one affecting Windsor, that might cost families their homes. Some opponents of same-sex marriage have turned this on its head and wondered if it will cost the government too much money. The answer, according to a Congressional Budget Office study, is that it most likely will not, both because the amounts, though large in the life of, say, a widow with a child, are not so large in terms of the federal budget. The government will also make money from things like imposing the income-tax marriage penalty on more couples, and from some people losing eligibility for benefits when their combined income is calculated. (There are harder-to-answer questions, like how much it might save Medicare if, earlier in life, a person had access to preventive care through a spouse’s insurance.) Marriage equality does not inflate budgets; it removes irrational distortions from them.

And that is why, if one believes in protecting free markets, then same-sex marriage should be a priority, too. This is the point that the amicus brief made with regard to recruiting. It hurts companies and the economy when the choice in taking a job at one firm or the other is not based on its salary offer or a belief in its prospects, but by whether it is based in a state the recognizes the employee’s marriage. It hurts, too, when a spouse who is a foreign citizen is not welcome here. And—something the corporate brief also mentions—there is the wedding business to consider, too. Last summer, New York City estimated that it gained two hundred and fifty-nine million dollars from same-sex marriages in the first year that they were legal in the state. “Marriage equality has made our city more open, inclusive, and free—and it has also helped to create jobs and support our economy,” Mayor Bloomberg said.

But there are less obvious ways that a failure to recognize same-sex marriage can reduce the transparency that helps the private sector thrive. For example, the Windsor brief notes that DOMA has the effect of exempting same-sex spouses of politicians and public officials from financial-disclosure requirements. It also denies them the protection of laws that, for example, make threatening the spouse of a federal agent a crime.

I.B.M. didn’t know it at the time, but it came close to losing Edith Windsor when, as her brief recounts, it “unwittingly ran afoul” of an executive order that forbade companies with federal contracts from having gay or lesbian employees—the order was issued in 1953, the year before the computer pioneer Alan Turing, who had faced similar barriers in Great Britain, killed himself by eating a poisoned apple. Luckily, the F.B.I. didn’t ask Windsor about the women in her life when interviewing her for a security clearance (to work on that UNIVAC), and I.B.M. didn’t find out, either; she wore a diamond pin, rather than a ring, as a symbol of her long engagement to Spyer. And then she left the company to care for a woman who, for many years, she could only say was a friend.