They reject that. Instead, they and Walker offer studies that purport to prove that it makes no difference whether or not a child has parents of both sexes. These academic studies are as unserious as all those academic studies of a generation ago that "proved" that boys do not prefer to play with trucks and soldiers but would be just as happy to play with dolls and tea sets, and that girls do not prefer dolls and tea sets but would be just as happy to play with trucks and soldiers.
These newer "studies" of same-sex parents are as valid as the earlier propaganda in the guise of scientific studies. Like the boy-girl studies, these were conducted by academics with agendas: the denial of male-female differences and the promotion of same-sex marriage. That many Americans believe these studies -- studies that are in any case based on a small number of same-sex couples raising a small number of children, during a short amount of time (a couple of decades), based on the researchers' own notions of what a healthy and successful young person is -- only proves how effectively colleges and graduate schools have succeeded in teaching a generation of Americans not to think critically but to accept "studies" in place of common sense.
Ask anyone who supports same-sex marriage this: Do you believe that a mother has something unique to give to a child that no father can give and that a father has something unique to give a child that no mother can give?
One has to assume that most people -- including supporters of same-sex marriage -- would respond in the affirmative. How, then, can they support same-sex marriage? The left's trinity -- compassion, fairness and equality -- is one reason. And "studies" and "facts" are another.
That is exactly how so many college graduates came to believe that boys would be happy with tea sets, and girls would be happy with trucks -- compassion, fairness, equality and "studies." That is also how many Americans, including a judge who overturned a state's constitutional amendment, have come to believe that never having a mother or never having a father makes absolutely no difference to a child.
And if mothers and fathers are interchangeable, men as men and women as women lose their significance.