J. Budziszewski noted that sometimes we deny what we know to be morally true by improperly pitting two moral principles against one another.  Consider marriage and fairness.  We recognize both to be moral goods.  Those who advocate for same-sex marriage, however, pit them against one another, arguing that if we are going to be fair we must permit same-sex couples to participate in the institution of marriage.

The problem is in their understanding of fairness.  They understand fairness to mean everyone must be treated exactly the same.  This definition is flawed, however.  Fairness requires that we do not arbitrarily treat people differently, or arbitrarily treat them the same.  In the case of same-sex marriage, we are not arbitrarily treating same-sex couples differently than heterosexual couples.  There is a principled reason for our discrimination: as a rule, heterosexual couples procreate while same-sex couples do not (and the principal reason government is involved in regulating marriage in the first place is because they are interested in the production and socialization of children).  To say it is unfair to preclude same-sex couples from marrying is like saying it’s unfair to allow one baseball team to beat another.  The purpose of baseball is competition, so it is fair to allow them to compete.  Likewise, the purpose of marriage is procreation, and it would be unfair to treat relationships that cannot procreate as equal to those that can.