and most of those in opposition to equality in marriage argue that every single couple are and should only get married to procreate.<quoted text>
Nor do opposite sex couples have to.....only sex between men and women is potentially procreative. Proponents of SSM are arguing from the standpoint that same sex personal intimate emotional sexual relationships are in fact marriages, even though there is still significant disagreement nation wide on this point, and seek to graft them onto the existing legal, cultural, historical, and/or religious understanding, and structure, of marriage as a union of husband and wife, including the body of laws that address that sexual union.
Marriage serves society by linking men, women, and their children together. Any deviations from this only serve to increase the instability of that function.
In a world that is already failing because we humans have over populated it, why make laws that married couples must have offspring?
That's like saying all pet owners must breed their animals. It just makes no sense to demand that people keep making more.