It is imperative for Catholics to develop rational arguments to defend the institution of marriage in the public square. We live in a pluralistic society and, therefore, what we accept as revelation is not necessarily accepted by others. However, an argument grounded in right reason—without explicit recourse to revelation—is in principle comprehensible to all persons of good will.
As we consider the current debate over marriage, it would be a mistake to underestimate the pedagogical function of the law and how a fundamental change in marriage law will result in a fundamental change in our understanding of the human person. What is at stake in the push to redefine marriage to include same-sex partners is not only the radical redefinition of marriage—but, also and necessarily, the radical redefinition of the human person and the entire range of relationships that constitute our basic experience as persons: male and female; husband and wife; mother and father; son and daughter; brother and sister.
Same-Sex Marriage Renders the Public Recognition of Marriage Unnecessary
Marriage between one man and one woman is recognized as a public institution, with its attendant benefits and responsibilities, precisely because it serves the common good. Marriage offers the State its most necessary common good: bringing children into the world and raising them in a family that includes the love of their mother and father. The State needs people (citizens) in order to flourish: no people = no State. Under the principle of subsidiarity, the common good is better served when mothers and fathers raise their children, not the State.
Extending marriage to same-sex partners will redefine marriage in such a way that marriage will no longer be understood to have a direct relationship to the procreation and education of children. Bringing children into the world and raising them will be seen as extrinsic rather than intrinsic to marriage. Openness to procreation will no longer belong to the very substance and definition of marriage. It will be reduced merely to an option for those couples who happen to want children.
Some might object that if we have proven anything, we have proven too much: if we were to insist that openness to procreation belongs to the very essence and definition of marriage, we would have to exclude not only same-sex partners from marriage, but infertile heterosexual couples as well. When examined carefully, however, this objection is not valid and does not hold weight. The sexual activity of an infertile heterosexual couple is intrinsically open to procreation—even though their sexual union cannot result in procreation. The sexual act of an infertile couple is the kind of act that is open to procreation; the fact that it cannot lead to procreation is accidental to the act itself. Under normal circumstances—i.e., functioning fertility—their act could lead to procreation. On the other hand, the sexual act of a same-sex couple is the kind of act that is never open to procreation; the non-openness to procreation belongs to the very substance and definition of that act.
Thus, one can rationally hold that openness to life is intrinsic to marriage without excluding infertile couples from marriage. Infertile heterosexual couples engage in the kind of act that leads to procreation; homosexual couples do not. A marriage comes into being not only though the exchange of the mutual consent of wills—as if we were disembodied spirits—but through conjugal, bodily union as well. A marriage, to properly exist, must be consummated: i.e., include the sexual union of spouses in an act which is open, in principle, to the procreation and education of children.
Redefining marriage to include same-sex partners would thus remove the essential public purpose of marriage from its definition: that is, the procreation and education of children. It thereby severs the institution of marriage from the common good. Yet, this would remove the very rationale for recognizing marriage as a public institution in the first place. The objection that legalizing same-sex marriage will have no harmful impact on heterosexual marriage is, therefore, shown to be entirely false. Such a redefinition of marriage would have the necessary effect of reducing all marriages to the status of private relationships with no relation to the common good. This, in turn, renders the public recognition of marriage as an institution utterly superfluous. To render a public institution superfluous is, of course, to undermine and call into question why the state should recognize and support that institution at all.
The Battle to Redefine Marriage Is a Battle to Redefine the Human Person
The move to redefine marriage will require us to reject the idea that women precisely as women and men precisely as men are essential to the relationship that is the foundation of all healthy societies: marriage and the family. Ultimately, those who want us to redefine marriage ask us not only to understand marriage as an essentially gender-less institution, but ask us to understand the entire range of relationships common to human experience as essentially gender-less. There is nothing less at stake in the marriage debate, therefore, than the battle to redefine our understanding of the human person and the relationships which constitute our experience.
This new understanding of the human person carries with it an implicit rejection of the body in its masculinity and femininity as a reality that is constitutive to our experience of personhood. It has, perhaps unwitting, the effect of alienating the body from the self and reducing the body to an object or instrument to be manipulated and shaped by what is understood to be an essentially androgynous consciousness. Under this view, the body is no longer affirmed as an always-already personal reality—a visible manifestation of the subjectivity of the human person. Rather, the body in dualistic fashion is reduced to the merely physical or animal level—i.e., to dumb, impersonal, biological matter. The dis-embodied person (subject) is then free to use the de-personalized body (object) as moved or inclined to do so.
Those who defend marriage as the life-long conjugal union of one man and one woman propose a different understanding of the human person and the body. The human person is seen to be a body-person, a composite-unity of body and soul (self-consciousness and self-determination). Under this view, the human body is different from an animal body not only in degree but in kind, because the human body is always-already a personal reality that cannot manipulated and used as a mere instrument. As body-persons, our bodies reveal and participate in our male or female personhood (subjectivity). When a man encounters a woman, he encounters a body that is different than his in her visible femininity, yet similar in that her body expresses personhood like his (and unlike animal bodies). In this sense, our common bodiliness serves as a visible affirmation of our shared humanity and our equal dignity as persons.
In a difference sense, however, the sexual differentiation of the male and female body serves another purpose: visible signs that accentuate the difference between man and woman in a way that highlights and affirms the unique dignity of woman vis-À-vis man (and vice versa). When a man encounters a woman, her body offers him limpid testimony that there exists another and different way of being human (female). This, in turn, gives visible witness to the man that he can never fully exhaust what it means to be human. He is limited and, furthermore, has no access to that other way of being human (female) unless the woman opens and gives him access to herself. The union of man and woman, then, is a unity-in-difference, a dual-unity in which it is precisely their difference that serves as the ground that makes their union possible. Moreover, this union is possible only on the basis of a mutual gift of self, the man to the woman and the woman to the man. Yet, even in their union, in their oneness, their personhood or identity is not absorbed or lost in the other. The very fruit of their union is an other—the child. And this other is, yet again, another visible sign of their unity-in-difference. The union between man and woman in marriage, then, is meant to be a union that is mutually enriching, that strengthens the identity of each even as it increases their oneness. Their union becomes all the more intimate as their uniqueness and difference is all the more affirmed by the other.
We who defend marriage as a life-long union of one man and one woman do so not with a spirit of animus toward those with same-sex attraction. Rather, we believe marriage should not be redefined because we are convinced that women bring something unique and irreplaceable to the marital relationship, something that men cannot—and vice-versa with respect to men. We also believe that women (mothers) possess a unique genius and offer their own special gifts to raising children—and vice-versa with respect to men (fathers). Further, we affirm that children have both the right and the need to experience the love of their mother and their father. Marriage between one man and one woman is the only form of marriage which provides children the ability to experience the love of their mother and father.
When a child’s biological mother and father are unable to care for him/her, we believe this is a great tragedy and sorrow. We try to remedy this sorrowful situation through the institution of adoption. Husbands and wives have the unique capacity to provide a home where adopted children can experience the love of a mother and a father. Yet, to redefine marriage is to purposefully deprive children the opportunity to experience the love of both a mother and a father. Two men might each be a good father, but neither can be a mother—and vice-versa for two women. The ideal for children is to experience the love of their own biological mother and father. Where this is not possible, children can experience the love of a mother and father through adoption. No same-sex couple can provide this experience for children. Therefore, no same-sex couple can provide for this common good of children and society.
In the end, there is more at stake in the marriage debate than appears at first glance. To redefine marriage to include same-sex partners severs marriage from the common good and, thereby, calls into question the very need for recognizing marriage as a public institution. By rejecting the idea that bodily difference (masculinity and femininity) is constitutive of the human person and is the indispensable ground for spousal union, those who push for the radical redefinition of marriage also and necessarily push for the radical redefinition of the human person. The force of law, then, will impose a fundamentally different understanding of those relationships which are most intimate to our human experience: male and female; husband and wife; mother and father; brother and sister.
 Even in the case of in-vitro fertilization or surrogacy, children become extrinsic to the marital relationship because a third (non-spousal) party must be introduced for conception to take place.
 The proponents of same-sex marriage argue that gender and race are equivalent: i.e., just as race is irrelevant to marriage, so too is gender. This is why they compare extending marriage to same-sex partners with Loving v. Virginia’s extension of marriage to different race couples. They equate race-less marriage with gender-less marriage.
 That is, a person is the kind of being who cannot be reduced to a mere object for use; therefore, because the human body is always a person-al reality, it too cannot be reduced to an object for use.