Society may no longer define marriage in the only way marriage has ever been defined in the annals of recorded history. Many societies allowed polygamy, many allowed child marriages, some allowed marriage within families; but none, in thousands of years, defined marriage as the union of people of the same sex.
It is essential that Christians understand this: Every Jew - secular, religious, assimilated, left-wing, right-wing - fears being killed because he is Jewish. This is the best-kept secret about Jews, who are widely perceived as inordinately secure and powerful. But it is the only universally held sentiment among Jews.