Well, "Yes and no" is the answer to the first question, "Yes, so long as there is a proper understanding of the common good" is the answer to the second and "Absolutely! For the sake of the individuals as well as for the sake of society" is the answer to the third. Let's take a look at these, particularly at the important qualifiers.
What is the common good? Marriage and family are the foundation of modern society and, as such, is inseparable from the common good. Love between a
man and a woman which brings about the procreation of children and the formation and continuation of communities both forming and formed by families. Today, when these basic realities are questioned and even redefined, it is crucial to rediscovering
their meaning and work toward re-establishing their basic structure.
As Pope Emeritus Benedict XVI wrote in his encyclical Caritas in Veritate, "The common good is “the good of ‘all of us,’ made up of individuals, families, and intermediate groups who together constitute society.” Every one of us contributes to the functioning of society as a whole, so we all bear some responsibility for the common good and should work together for it.
Marriage serves the individuals in the supporting union of husband and wife, but it is probably best understood when viewed in terms of the child. A child is formed from the relationship of a man and a woman and - ideally - is raised within this relationship. Here, a child learns what it means to live, love, and forgive. While no family is perfect, a family built upon the solid foundation of lifelong marriage provides something for a child that no other relationship or institution can: a mom and a dad united in the covenant of marriage, the spouses selflessly giving and trustingly receiving from each other. In order to understand the essential contribution that marriage makes to the common good, it is vital to recognize that marriage is the only institution that unites a man and a woman together and to any children that come from their union: it is the basis for the child's development of their own identity, their role within a larger unit (first the family then, gradually through larger groupings, society as a whole), and ultimately their definition of the common good. It is therefore a matter of justice to that child for marriage to form and sustain that definition.
Family structure matters. Numerous studies* show numerous positive outcomes for children of healthy, intact marriages. A married mom and dad still offer the best context for child well-being and development. Healthy marriages model so many virtues and good habits that are vital for social life. In other words, the joyful and sacrificial love between a man and a woman in marriage serves as an example to their children of what it means to love other people in general.
A healthy marriage culture is one of the best anti-poverty measures in existence. States in which there are more marriages are wealthier states; marriages seem to encourage economic mobility and lead to less child poverty. Breakdowns in these vital areas wind up costing the state (and taxpayers) billions annually and do harm to the common good.
So what is the state's role in this? What is the Church's role in this? Although carried out in the actions of individuals, the state has a major responsibility for the common good. As the U.S. Conference for Catholic Bishops states in its publication Forming Consciences for Faithful Citizenship, “the common good is the reason that the political authority exists.” This builds from an earlier statement made by Pope St. John XXIII: “the whole reason for the existence of civil authorities is the realization of the common good . . . every civil authority must take pains to promote the common good of all, without preference for any single citizen or civic group.” The state should be concerned for the welfare of all, and the structures and legislation that civil groups set up should reflect this concern. As the U.S. bishops have said, “How we organize our society—in economics and politics, in law and policy—directly affects the common good and the capacity of individuals to develop their full potential.”
Marriage is an irreplaceable part of civil society. Debates focus on questions of equality and fairness—values that are important to any society. But what these debates have often missed is the fundamental question: What is marriage? Before we can talk about equality or fairness in an institution, we must define what the institution is. Then, why has the state been—and why should it be—interested and involved in recognizing and supporting marriage? The answer to the second question depends the meaning of marriage. If marriage is solely about the romantic relationship of two adults, why should the state care? The state has not been in the business of recording and defining friendships or any other type of relationship on the basis of the degree of affection or level of commitment. In fact, we would probably think that was intrusion by the government into our private lives. However, marriage affects the culture in ways that extend far beyond the individuals concerned. In the ways just outlined and more, the state of marriage has profound implications on the surrounding society. Marriage uniquely contributes to the common good.
And this is definitely something that demands the support of the Church. Pope Francis challenged young people at World Youth Day 2013: “Today, there are those who say that marriage is out of fashion . . . They say that it is not worth making a life-long commitment, making a definitive decision, ‘forever,’ because we do not know what tomorrow will bring. I ask you, instead, to be revolutionaries . . . yes, I am asking you to rebel against this culture that sees everything as temporary and that ultimately believes you are incapable of responsibility, that believes you are incapable of true love. I have confidence in you and I pray for you.”
* W. Bradford Wilcox, “Even for Rich Kids, Marriage Matters,” Family Studies, December 19, 2013; “Why Marriage Matters, Third Edition: 30 Conclusions from the Social Sciences,” Institute for American Values, 2011.
Wilson and W. Bradford Wilcox, “Bringing up Baby: Adoption, Marriage, and the Best
Interests of the Child,” William and Mary Bill of Rights Journal. Vol. 14, No. 3, pp. 883-908, February 2006.
David Ribar, “Why Marriage Matters for Child Wellbeing,” The Future of Children. Vol. 25, No. 2, Fall 2015.
Paula Fomby and Andrew Cherlin, “Family Instability and Child Well-Being,”
American Sociological Review. Vol. 72 (2007): 181–204, article DOI (digital object identifier): 10.1177/000312240707200203.
Wendy Manning, Pamela Smock, and Debarun Majumdar, “The Relative Stability of Cohabiting and Marital Unions for Children,” Population Research and Policy Review. Vol. 23 (2004): 135–59, article DOI (digital object identifier): 10.1023/B:POPU.0000019916.29156.a7.
Kathleen Ziol-Guest and Rachel Dunifon, “Complex Living Arrangements and Child
Health: Examining Family Structure Linkages with Children’s Health Outcomes,” Family Relations. Vol. 63 (2014): 424–37, article DOI (digital object identifier):10.1111/fare.12071.
D. Paul Sullins, “Invisible Victims: Delayed Onset Depression among Adults with Same-Sex Parents,” Depression Research and Treatment. Vol. 2016 (2016); D. Paul Sullins, “Emotional Problems among Children with Same-Sex Parents: Difference by Definition,” British Journal of Education, Society and Behavioural Science. Vol. 7, No. 2: pp. 99-120, 2015.
Mark Regnerus, “How different are the adult children of parents who have same-sex
relationships? Findings from the New Family Structures Study,” Social Science Research. Vol. 41, No. 4, July 2012, pp. 752–770.