According to the link below, opponents of same-sex marriage will argue before the Supreme Court heterosexual marriage is the traditional definition of marriage, gay marriage is not. They will argue tradition rules, laws don’t.
It is true, for most of U. S. history the concept of marriage has been between heterosexual people, but many other things we would call tradition have been cast aside in favor of equal treatment.
Some of us are old enough to remember a phrase that was once so important it was thought to be more important than law. The phrase was, “Our Southern way of life”.
This phase was code language for segregation. The “Southern way of life” was separate schools, water fountains, swimming pools, churches and black people eating in the parking lots of restaurants instead of the dinning rooms.
Equal treatment under the law is in the Constitution, segregation is not. But, from the Southern point of view, something called the”Southern way of life” trumped the Fourteenth Amendment.
Today’s version of “Southern way of life” is “marriage has always been between one man and one woman.” That the financial and social benefits of marriage are not available to gay people is less important than this new version of the “Southern way of life”.
I would guess it is this argument about “tradition” that motivated President Obama, the Clintons, Republican Senator Rob Portman and others to endorse gay marriage. These make the case straight marriage is not seen by everyone as the only tradition in town.