Here’s an important section of a book everyone should read, What Is Marriage? Man and Woman: A Defense

So it is a summary, but hardly an exaggeration, to say that civilization depends on strong marriages.

Maggie Gallagher captures this insight with the slogan that “sex makes babies, society needs babies, and children need mothers and fathers.” She develops the idea: “The critical public or ‘civil’ task of marriage is to regulate sexual relationships between men and women in order to reduce the likelihood that children (and their mothers, and society) will face the burdens of fatherlessness, and increase the likelihood that there will be a next generation that will be raised by their mothers and fathers in one family, where both parents are committed to each other and to their children.”

Even now, this claim is not partisan. Thus David Blankenhorn, a liberal Democrat:

“If you’ve been trained, as anthropology field researchers typically are, to begin at the beginning—to start with the most fundamental issues—you will report a cluster of related facts: Humans are social; they live in groups. They strongly seek to reproduce themselves. They are sexually embodied. They carry out sexual (not asexual) reproduction. And they have devised an institution to bridge the sexual divide, facilitate group living, and carry out reproduction. All human societies have this institution. They call it ‘marriage.’”

Girgis, Sherif; Anderson, Ryan T; George, Robert P (2012-11-27). What Is Marriage?: Man and Woman: A Defense (pp. 38-39). Encounter Books.