First, marriage is not about equality. Marriage is about setting norms for society for how we structure sexual relationships, for creating cooperative and respectful domestic relationships between the sexes, and for forming families for raising children. Anthropologist Suzanne Frayser, after studying the role marriage plays across diverse civilizations, offers this universal definition: "Marriage is a relationship within which a group socially approves and encourages sexual intercourse and the birth of children." Edward Westermarck, who has written an immense three-volume history of human marriage, agrees. He says marriage is always about bringing forth the next generation.
Glenn T. Stanton and Dr. Bill Maier, Marriage on Trial: The Case Against Same-Sex Marriage and Parenting, pg.34-35