Opponents of gay marriage have marshaled a number of good arguments in support of the proposition that marriage is no more and no less than the union of a man and a woman for life. And for the most part I agree with them.
Yes, marriage was instituted by God, not originally defined by the laws of men. Yes, it is a holy mystery for the faithful to contemplate, not just a legal contract or a social status. Yes, it is a reflection of the relationship between our Lord (as the Bridegroom) and the church (as His bride), which we mock at our peril. Yes, it is a divine calling which only God can consecrate. Yes, it is a matter for church, not state. It is a matter pertaining to the free exercise of religion, which the U.S. Constitution protects from government meddling. Yes, it is the most proper, right, and beneficial basis for the begetting and upbringing of children.
Community property, pensions, survivor benefits, and so forth are only so much window dressing added by the cumulative custom of our society and its laws; and those customs can be observed without marriage. But the faithful have a right to believe and cherish the faith that has been handed to them, including the article of marriage as God created it and intends to bless it.
Now I have a thought I would like to add to all this. I speak as a never-married bachelor a couple years shy of 40, one who never intended to be celibate for life, one who still dreads the effort of doinng so, and one who sees the likelihood of any God-pleasing alternative dwindling to nil. Becoming gay would sure be easy. I know a lot of gay guys; I'm a Symphony groupie, remember? They seem to be lovely people. It wouldn't be hard to hook up with someone who shares the same life energy, the same taste, maybe even the same general way of thinking. The more we had in common, the more stable and long-lasting the relationship would probably be. But at bottom, what I would I get out of it that I couldn't have all by myself? Therein lies the flaw, I think, in the very best gay partnership imaginable: the essential ingredient of narcissism.
My theory is that only one type of life partner can bring out the best in a man: a woman. And though I don't have much direct experience with the female sex, I reckon the reverse is equally true. Men and women need each other because they are so different, so opposite to each other at the deepest level. Even butch women are profoundly unlike men in character and mentality. And most so-called "effeminate" men think and behave in a way distinctly different from most women. Experience confirms this. Have you ever known a woman who really acted like a gay man? In my whole life I only met one--an experience whose strangeness goes right to my point. Men and women think so differently that they are like alien life forms to each other, an eternal and unsolvable mystery--fascinating at best, irreconcilable at worst, sometimes a danger to each other, sometimes both immovable and irresistable at the same time.
I believe, in spite of having observed some of the worst man-woman relationships in the free world and having personally participated in zero, that each sex's key to the highest happiness lies in an ironclad promise to become "one flesh" with the other. I believe that the madness and frustration each spouse must feel in learning to communicate with the other is far from a reservation against this theory, but rather goes straight to the point of it. We need our opposite in order to bring out the best parts of ourselves and to temper the worst parts. We need to be forced to accommodate our life-habits, thought-forms, and heart-language to someone completely different. We need the person we cuddle with in the wee hours to be the one who shakes us out of our comfort zone so that we may truly learn what it means to love, to give, to serve, to forgive, to be kind, patient, self-controlled, faithful, gentle, humble, etc.
Marriage to a partner of the opposite sex is guaranteed to teach that lesson, even if the student refuses to learn it. Partnership with someone "just like me," however, isn't marriage. It's self-abuse by proxy. It's self-indulgence. Sooner or later, at least one member of the partnership must realize that each of them has done nothing but feed his own, or the other's, narcissism. And then it will be over, and another partnership just like it may take its place because no lesson will have been learned.
It's as if marriage (man + woman) is God's school to teach us to be complete human beings. In my opinion, no one who hasn't graduated from that school should be allowed to raise new human beings. But even if no one listens to my opinion on that, I believe God's opinion on the usefulness of the man and woman becoming "one flesh" must not be lightly set aside. To do so would be to privilege a class of incurable narcissists' feelings of self-worth in preference to the whole society's right to think, believe, and judge as they choose about matters that lie outside the competency of any judge or civil servant. To do so would be to privilege chronic self-abuse above one's opportunity to be challenged by the ways and thoughts of the other, the opportunity to form a synthesis with them so as to become more than the sum of our parts.