Distortion

Have you seen this graphic circulating around facebook?  I saw it in the context of the gay marriage debate - the underlying message being: "There's no such thing as traditional marriage.  You can't say it's the exclusive union of one man with one woman unto death, because there are so many forms of "traditional" marriage that are sanctioned in the bible!  Look at them all."

No doubt if I've misrepresented the implication, someone will correct me politely in the comments below.  But I don't think I have.

This approach is either ignorant or deceitful - the creator of the graphic has either misunderstood what the bible says about marriage (and all the distortions of it); or they have deliberately misrepresented it to bolster their position.  Here are some problems with the argument:

1. No Christian arguing for traditional marriage is arguing for marriage practices that happen to have existed at some time in human history.  They are arguing for marriage as it has been created and sanctioned by God.  They recognise that people, including people in the bible, fall short of God's standards.  This includes God's standards for marriage.
   So mere appearance of a practice in the bible is not an indication of approval of that practice.   Otherwise we would defend adultery (King David and Bathsheba) and murder (David doing in his rival Uriah, Bathsheba's husband).  No reasonable person would argue that these practices are sanctioned.  Similarly, one cannot argue that polygamy or concubinage or taking the slave of one's wife is sanctioned in the bible, particularly in light of Jesus' affirmation that marriage is one man, one woman, one lifetime!
   Yes, God can choose to bless sinners in polygamous or concubinous relationships, just as he blessed the adulterous and murderous David.  Yes, he uses them to fulfill his purposes.  But this is not an indication of his approval of their sin.  It's an indication of his astounding grace in loving people who rebel against him again and again.
2. The graphic confuses the marks of marriage with the motivations for marriage. This is a common mistake in the marriage debate - arguing that marriage is all about love, and that therefore two people in love should be able to marry regardless of gender.  The problem is that one motivation for marriage (love) is confused with a mark of marriage. 
   The "info"graphic represents different motivations for marriage: some of them bad , some more honourable, but none of them touch the marks of the marriage:

• The graphic imports some extraneous rules about marriages into its description of marriage.  So in the "man + woman" box, there are a number of dot points which describe various cultural practices or religious laws that were connected with marriage.  But these practices and rules have always varied.  They continue to vary - take the change in divorce laws as an example, or the tendency to marry for love rather than economic reasons.  What hasn't varied is the description of marriage as one man united exclusively to one woman for as long as they both live.
• The requirement for a man to marry his brother's childless widow is designed to ensure continuity of the brother's name, and provision of support for the widow in later life.  The motivation to marry reflects an imperfect situation.  It solves a social problem in a way that we do not condone today.  But the institution is still a marriage - one man with one woman.
• The requirement that a rapist marry his victim was a merciful requirement - otherwise, rape victims likely would never have married, as no man would have her.  Although the motivation for marriage is to make the best of a bad situation, the marriage itself would not differ at all from other marriages.
• Similarly with the prisoner of war situation - in circumstances where women were likely to be prey to the rape and pillage of an invading army, requiring marriage gave a woman some protections.  Again, the motivation to marry is likely just lust and self-interest, but the marriage would still be one man, one woman.
• The situation of slaves would have been the same.  Although the parties had little to no choice in the matter, the marriage was recognisably the same as a marriage contracted between two people for other reasons, whether economic, socio-political or emotional.

No, the assertion that there is no "traditional" marriage is either ignorant of history, or is a willful, deceitful distortion of the truth.  
Sure, there have been many examples of people falling short of marriage, either through multiple marriages (concurrently or consecutively), or through adultery, or through cruelty and abuse.  
Sure, there are many marriages that are contracted for motives that we abhor today.  
Sure, the ideal of marriage is something that we frequently strive after, but rarely attain.  
But there certainly is a commonly held, historically grounded understanding of what marriage is.