Argument: Children do better with mother and father role models
David Blankenhorn. "Protecting marriage to protect children." LA Times. September 19, 2008: "Marriage is society's most pro-child institution. In 2002 -- just moments before it became highly unfashionable to say so -- a team of researchers from Child Trends, a nonpartisan research center, reported that "family structure clearly matters for children, and the family structure that helps children the most is a family headed by two biological parents in a low-conflict marriage."
All our scholarly instruments seem to agree: For healthy development, what a child needs more than anything else is the mother and father who together made the child, who love the child and love each other."
Brad Sears & Alan Hirsch "Gay Marriage: Pro and Con" UCLA Law School's Williams Institute 11/26/03 - "The notion persists that gay couples make poor parents because they are inadequate [differentiated] role models. The new variation of the argument is suggested by the quotes  from  conservative pundits: Children need a parent of each gender to model appropriate behavior. In [the supreme court case] Goodridge, the state advanced this argument in opposition to same-sex marriage. Kristi Hamrick of the Family Research Council puts the point bluntly: 'A child needs a male role model and a female role model. These are not interchangeable puzzle pieces.'"
Adam Kolasinksi's, "The Secular Case Against Gay Marriage" 2/20/04: "there is ample evidence (see, for example, David Popenoe's Life Without Father) that children need both a male and female parent for proper development. Unfortunately, small sample sizes and other methodological problems make it impossible to draw conclusions from studies that directly examine the effects of gay parenting. However, the empirically verified common wisdom about the importance of a mother and father in a child's development should give advocates of gay adoption pause. The differences between men and women extend beyond anatomy, so it is essential for a child to be nurtured by parents of both sexes if a child is to learn to function in a society made up of both sexes. Is it wise to have a scoial policy that encourages family arrangements that deny children such essentials? Gays are not necessarily bad parents, nor will they necessarily make their children gay, but they cannot provide a set of parents that includes both a male and a female."
Boston Globe columnist Jeff Jacoby warned in 2003 that the Massachusetts decision imperils "unique sex roles in family life."
Professor Douglas Kmiec, LA Times - Children of gay parents miss "the benefits of child rearing by the distinct attributes of both father and mother."
Dr. Rick Fitzgibbons of Catholic Medical Association 7/20/05 said that the Americans Psychiatric Association's 2005 call for the legalization of gay marriage "ignores the vast scholarship on the needs of children such as Henry Biller's 'Fathers and Families: Paternal Factors in Child Development,' which includes a bibliography of almost 1,000 separate articles or books on the positive effects of fathers on children."
Christopher Ott. "Banning same-sex marriage would protect no one." Progressive.org. February 8, 2005: "In 2002 -- just moments before it became highly unfashionable to say so -- a team of researchers from Child Trends, a nonpartisan research center, reported that 'family structure clearly matters for children, and the family structure that helps children the most is a family headed by two biological parents in a low-conflict marriage."