Same-sex marriage teaches children and their generation that marriage is merely about fulfilling adult sexual and emotional desire, nothing more. Many approaches to and philosophies of heterosexual marriage already teach this, and same-sex marriage will only help solidify it.
Same-sex marriage—like easy divorce, cohabitation, pre- and extramarital sex, and unmarried childbearing—relativize family relationships. It promotes a smorgasbord mentality for family life: choose what suits your tastes, and one choice is as good as another. But no society has ever been able to sustain itself with such a view of family life.
Same-sex marriage will teach little boys that the idea of being a good family man—caring and sacrificing himself for one woman and their children—is not expected or even virtuous, but merely one lifestyle choice among many. Same-sex marriage teaches our daughters that being committed to and helping socialize a husband and bearing and raising children with him is only one family lifestyle choice among many.
In short the entire meaning and significance of marriage itself, and what it means to be male and female, will be radically changed. So will the choices and behaviors of those who grow up within that altered social context.
Glenn T. Stanton and Dr. Bill Maier, “Marriage on Trial: The Case Against Same-Sex Marriage and Parenting,” pg.55-56