In order for a culture to accept homosexual practice as a cultural norm, people need to sever the link between enjoyment and purpose.
It is easy to see why people want to turn the question of homosexual marriage into a civil rights case. People should be free to marry whoever is preferred - society and its government shouldn’t be able to interfere in the personal lives and loves of its people. It is such a basic thought that to question it is to question both individual freedom and the very institution of marriage. God, rather than being a Designer with our best interests at heart, seems to become a cosmic kill-joy, creating people with desires they cannot satisfy. It seems we should oppose this limitation on principle, even if it doesn’t apply to us personally.
But on the contrary, God’s design of us must make us reconsider. Even if my opponent has dismissed the possibility of God himself, he can’t ignore the very specific practical purposes of the “hardware” we have each been given. (on a side note, it is not surprising that in a world that believes only in the physical, when the physical reflects a Designer, the first response is to ignore it, and if it cannot then be explained away, the next option is surgery...in any case, the physical MUST not be allowed to stand in the way of personal gratification.) In order to embrace (forgive the pun) the homosexual life as culturally acceptable, we must disengage the passionate experience from the purpose. If the sexual climax becomes the goal of the act, then who is to say that there is only one way to accomplish it? Why not two men? But with this reasoning, why should one stop there? Why not 3? Or with machines, or animals, or children? By rejecting the idea that the male is made for the female and vice versa, and separating the experience of sex from any sense of purpose for the act beyond momentary pleasure (building relation between husband and wife for raising the children they make; literally making the children; forging links in the generations of an extended family), we have become sexual anorexics. We like the taste of the food, but we reject (and eject) the nourishment. Imagine a culture that spent all of its time preparing and chewing the finest of foods but never swallowing. Wouldn’t that group eventually have to find ways to artificially ingest nourishment? IV lines into the arms, taking vitamins... and wouldn’t they necessarily have increased illnesses, physical and emotional? Is our culture not that way to a degree already? If we divorce the connection between nourishment and pleasure we will misunderstand the entire eating process. The same is true of sexuality. If we disconnect the pleasurable experience from the function, we will misunderstand the entire plan and purpose.
And it is no good claiming this is only a problem with those who practice homosexuality, it is just as much a problem for those heterosexuals who have made this separation. To indulge the pleasure of the moment without a knowledge of the purpose of the act is like clear-cutting forests or strip mining land. We want the profits and don’t care about what we do to our selves, our partners, or our homes. In each case, we need a re-grounding in the design of the Designer, and a reminder about how we are to both tend AND keep the world we have been given: tending means to help it come to fruition, and keeping means to protect and cherish.
When two men decide to care for one another in the way of husband and wife, they are not only going against the physical evidence, they are misunderstanding the nature of marriage. Marriage is the harmonizing of two people. Harmony in music (at least since 1100) can only happen when there is more than one pitch: a unison is not harmony. Two of the same gender cannot create harmony, harmony requires difference. And it is interesting that when two different pitches are tuned properly they generate overtones - some of which are actually new pitches, not merely octave representations of the original two.
What’s more, the greatest example of harmony is to be found within the Trinity. There, the three Persons have been in harmonic relation throughout eternity, making one single God able to love and relate in harmony, not unison. There are not three Fathers, or three Sons, or three Spirits -- there is one of each, and they have specific relations and roles they each play in relation to each other. Marriage is designed to be an imitation of that relation: a harmony of one made up of two different ones, and that cannot be accomplished if the two are of the same gender.
For those who look on reality from a sentimental point of view, it may seem harsh or unkind to put limits on the definition of marriage when it means that many desires will go unsatisfied. But surely this is a view that places individual desire above reality? Don’t we have rules that keep peoples’ desires in check in other arenas of life? Don’t we say that it is wrong to have sex with minors? (there are those trying to change that too, by the way, and on the same principles) and don’t we say that it is wrong to favor your own gender or race above others in court or business hiring? Why should those desires, preferences, and inclinations be limited when sexual desires are allowed free reign?
Why do you suppose past generations have been so clearly against homosexual practice? Could it be that they understood the design of the world better than we do, and, like the reasonable ban on adultery, knew that certain practices, if allowed free reign, would destroy the society?