The simple answer is as follows: If invited to such a ceremony, as stated above, one should decline, responding, “My religious beliefs hold that marriage is between a man and woman, and therefore I will not be able to attend,” or simply saying, “I have other commitments,” that being to God’s law.
Every Christian needs to understand the foundation for this answer. Marriage is between a man and a woman, and their conjugal love is both unitive and procreative. The beautiful stories of creation in Genesis as well as the teachings of Our Lord (cf. Mt 19:3ff) on marriage attest to this truth. Even for an unbeliever, reason alone dictates that a man and woman are complimentary, i.e., made for each other, and that marriage and the marital act are inseparable from the procreation of children and the continuation of the human race.
The emphasis on children must not be lost. Children have a mother and a father whom they want to know and whom they have a right to know. A person’s family— Mom and Dad, siblings, grandparents, and others — provide identity. Also, stable marriages and families build a stable society. A homosexual couple, however, either has to adopt or conceive a child through some sort of reproductive technology that supplies donor sperm, donor ovum, or both, and maybe a surrogate mother. While some, in the pursuit of their own selfish interests, may argue, “It doesn’t really matter as long as we love the child,” the reality is it matters to the child, who eventually asks, “Who is my mom? My dad? My ancestors? Where did I come from?” Also, society ought to be concerned over the future impact of these practices in general. Recently, a young man in California who was manufactured by his natural mom and sperm-donor dad discovered that he had more than 150 siblings; have we considered the impact on society when intermarriage will occur unknowingly, i.e., a man marries his sister unknowingly?
Finally, the act of homosexuality is intrinsically disordered and is a mortal sin. The Catechism of the Catholic Church teaches clearly: “(Homosexual acts) are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved” (No. 2357). Sacred Scripture condemns the depravity of homosexual acts (Gn 19:1-29, Rom 1:24-27, I Cor 6:10, 1 Tm 1:10). Consequently, individuals inclined toward a same-sex attraction are called to live a chaste life, as are all people.
Nevertheless, as Christians we treat all people with dignity and respect. The church’s teachings reflect this position: “Pastoral care of such homosexuals should be considerate and kind” (“Declaration on Certain Problems of Sexual Ethics,” No. 8). “They must be accepted with respect, compassion and sensitivity. Every sign of unjust discrimination in their regard should be avoided” (catechism, No. 2358). “It is deplorable that homosexual persons have been and are the object of violent malice in speech or in action” (“Letter on the Pastoral Care of Homosexual Persons,” No. 9). Therefore, while condemning the sin (i.e., the act), and upholding the sanctity of marriage and the rights of children, we treat the sinner with dignity and respect.
Undoubtedly, the issue of “same-sex marriage” or “civil unions” increasingly will confront faithful Christians. Regularly, The Washington Post prints pictures in the wedding section of homosexual couples. A cable television show called “The New Normal” is based on a homosexual couple raising children. This “in-your-face” strategy coupled with the brain-washing of our children in public schools about what is a marriage and what is a family will eventually make the moral debate banal.
Christians, however, must continue to uphold, defend and teach what is true and good in the eyes of God, as we know through both divine revelation and reason itself. To witness some kind of same-sex commitment ceremony would be to give tacit approval for something false and disingenuous, and could scandalize others, especially young people. Finally, a Christian prudently needs to keep certain boundaries and be careful how close he becomes to a person who does not share the same faith and values.