In what natural law theory regards as a rightly ordered society, most people marry, and marriage typically results in children, and lots of them. This in turn creates a large social network of people known personally to one – lots of brothers and sisters, cousins, aunts and uncles, and so on – on whom individuals can fall back in times of need. Divorce is stigmatized, so that children generally have stable homes and discipline, and they and their mothers generally have a reliable provider. Elder family members are looked after by the new generation, just as they looked after that generation when it was in its infancy. Elder members also find ongoing purpose in helping to raise their grandchildren. In general, the good of the family takes precedence over the desires of the individual member. And this subordination of self-interest to the common good of the family makes people more sober and realistic in their expectations, less selfish, and better able to achieve a contentment that is deep and lasting even if not as titillating as running off to begin a second or third marriage.
Contrast that with the contemporary mentality, which regards sex and romance as primarily a matter of self-fulfillment, rather than having self-sacrifice for the sake of children and family as its natural end. Whereas the traditional arrangements commended by natural law subordinated the short-term interests of the individual to the long-term health of the family, the modern mentality subordinates the long-term health of the family to the short-term interests of the individual. Naturally, solidarity is weakened [and this weakened solidarity extends to the society as a whole].
Edward Feser, “Liberty, equality, fraternity?“, Edward Feser blog, October 10, 2017.