Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America By Jonathan Rauch Times Books, 224 pages, $22

If homosexual marriage is ever democratically (as opposed to judicially) legislated, it will be because of the case made by individuals like Jonathan Ranch. In Gay Marriage, Ranch eschews legal and liberationist assertions and instead argues on the merits that homosexual marriage is, as his subtitle maintains, good for gays, good for straights, and good for America.

The book's great virtue is its straightforwardness. Ranch's first chapter asks: What is marriage for--why does society privilege marriage legally? His threefold answer is: to provide a healthy environment for children, to settle the young (especially men), and to provide reliable caregivers (especially in the case of catastrophe). Ranch assumes such interests are severable--that is, raising children can be separated from marriage as a domesticating and care-giving institution. This allows him to leave children out of his definition of marriage: the legal recognition of two people's lifelong commitment to care for each other.

For obvious reasons, Rauch emphasizes domestication and care-giving in his case for same-sex marriage. Gay marriage, he asserts, would make gay men grow up. Within a generation or...