If the members of these groups mean by "origins" the "union" so poorly described in Genesis from which man "fell" from grace, they have painfully little by which to comprehend the basis or nature of that union. There is considerable reference within the scriptural record to the spiritual union of one man and one woman, but an acute shortage of important detail. One of the unspoken missing links within institutional Christian tradition is the absence of any insight into that union which once brought a man and woman into direct contact with the living God, without any of the institutional forms that are found necessary today.
Even after two thousand years of scholastic theological exegesis, tradition is unable to describe with precision not only the nature of the union described in Genesis, but that of the single transgression which left man in his fallen state. It is this fall and its resultant state that many would agree remains key to an understanding of human nature today.
One curious religious teaching on marriage, now wearing so thin as to be transparent, is the "natural law" concept that human "sexuality" is a spiritual "gift" of God. This concepts begs the question of how an unruly instinct of biology, one outside human volition, for the most part irrational, and itself a material reality, can be either moral or spiritual. The idea that a potential of biology, called euphemistically "procreation," adds to a relationship some moral or spiritual advantage from God is dubious indeed. Carnality existed long before any of the monotheisms ever appeared on earth, and biology isn't changed either by contrivances of language, ceremony and blessings, or by the most sincere aspirations of a man and woman.
That skepticism is fully justified when one considers the frequent effects of sexual infidelity: porn, prostitution, divorce, broken homes, unwanted children, overpopulation, sexual abuse and violence, rape, AIDS, other sexually transmitted diseases, contraception, abortion, possible links to testicular and prostate cancers, DNA degeneration in sperm, implications for the immune system, and even female vaginal conditions. Given such huge costs to human well-being, both individually and culturally, one would think it is time to seriously question the spiritual basis of sexuality and see it more as the human expression of animal life on the farm. Unfortunately, this is the point in thinking about the subject at which human pride kicks in and honesty and rationality fall into the abyss. But, in confusing the biological imperative we call sex for a spiritual expression of love, aren't we simply engaging in intellectual prostitution and falling into the "sleep of reason"? Probably so. And isn't it just more wishful thinking when religious people hold fast to the idea that "we" are "created" in the "image and likeness" of God without being able to convincingly define that likeness, moral or spiritual? Still, the whole of existing religious identity rests on that assumption.
What we are up against is that, however appealing that assumption might be, it doesn't square with reality. That can be plainly seen in the growing environmental crisis that is quickly tearing our planet to pieces. Our tragic failures as stewards of the earth cannot possibly reflect the wisdom of God, nor can we truly be His children while we remain so self-evidently a destructive and unsustainable species.
Of course, the existence of such a single Law would change the very nature of religion itself--from the top-heavy temple/church traditions we observe in the world today to an individual spiritual-virtue ethic founded within the marriage of one man and one woman. Such a Law would eliminate the need of any institutional support at all, and be fulfilled simply by means of human integrity and fidelity to new moral purpose. Sound like revolutionary stuff? Maybe that's what put Christ on the Cross!
Today, marriage between a man and a woman, as an ideal of a kind of relationship that should be...simply isn't! This aging institution desperately needs new foundations that religion has failed to provide. Let's assume there is a God and that He wishes to make a spiritual union between a man and a woman pre-eminent over all others. To do so, He'd need to try something just a little different: create a foundation of divine wisdom that "lifts" the spirit of man to a new understanding of both God and the very nature of Love. The effect would be a "Resurrection" that reduces the dualism in the human condition into a unified whole.
I couldn't find that "key stone the builders rejected" anywhere in the Bible. But Shakespeare appears to have a better idea than most religious people of what it might take to straighten out the human heart! Quoting from his poem "Venus and Adonis":
Call it not love for Love to heaven is fled
Since sweating lust on earth usurped his name.
Under whose simple semblance man has fed,
upon fresh beauty blotting it with blame,
which the hot tyrant stains and soon bereaves
as caterpillars do the tender leaves.
Love comforteth like sunshine after rain,
while lust's effect is tempest after sun.
Love's gentle spring doth always fresh remain,
lust's winter comes ere summer half be done.
Love surfeits not, lust like a glutton dies,
Love is all truth, lust full of forged lies.