We are apparently to choose between the spurious claim that any two people who engage in sex should be entitled to the benefits of marriage as option 1, and the equally spurious claim that the monogamous family unit was divinely prescribed as option 2. The buzz-term ‘marriage equality’ comes with the first, which if taken all the way would mean allowing any two people to marry, so goodbye to consanguinity restrictions and the age of consent. With the second comes the warning that SSM would lead us down a slippery slope to polygamy. They really should have a look at Sharia law some time!
Marriage as a legally recognised social institution has been around for a very long time. The ancient law-writers such as Hammurabi did not invent the husband/wife relationship any more than they invented the employer/employee or doctor/patient relationship but formalised customary law related to it within an emerging legal framework. For the origins of marriage as we have understood it for thousands of years, we would probably have to go back to the early city-states when people needed to pass property and title to their rightful heirs, for which certainty of parentage is a prerequisite – hence the institution of marriage. The ages-old strong relationship between marriage law and inheritance law is no coincidence. (Depressingly unromantic stuff, I’m afraid.)