It is in one good and important sense at least. People had to adapt to these things as best they could. It could and should be changed to meet changing human needs. I see this book doing some of that important transformative work. Through the testimony of experience and with the power of story, the author gives ample evidence that heterosexuals have no monopoly on the reality of marriage.
Marriage is meant to be inclusive regardless of sexual orientation.
Because the essence of marriage is not biological procreation it is love. Jeremy Taylor, for example, was one Puritan-influenced Anglican divine who challenged both the sentimentalism and the cynical commercialism of marriage in his time. Taylor held that deep affection, mutual respect, and friendship were of the essence in a true, lasting marriage. Sexual intercourse, he believed, had a great capacity to endear the partners to each other. That was its primary purpose.