There are absolutes. Proverbs puts it thus "Remove not the old landmark; and enter not into the fields of the fatherless".
The old landmarks include the basic -- self-evident to the Founder's generations -- definitions of marriage, of murder, of life, of WHO IS A MAN. Justice Tanney busted down that last old landmark, and as a consequence a most bloody civil war ensued.
A state can place some constraints on what constitutes a legally recognizable marriage, or define categories of murder. But there are some limits to the ability to redefine basic concepts and terms of law.
The modern folly of redefining marriage is as bad or worse than what Justice Tanney once did.
Well, I think marriage is a states issue. I don’t think the U. S. Constitution permits the federal government to meddle with marriage.