Not really.
The Romans and Greeks, for example, were largely if not perhaps exclusively monogamous.
Well no.
The default has always been one man and one woman at a time with everything else being an exception to the rule.
Even in societies where polygamy was allowed there were major rules about the circumstances that the multiple marriages were legitimate.
Kings and rulers were allowed more often then most because marriages were to seal alliances. But even in that there was usually a "great" or "first" wife who was the "real" wife with all others being given the status of legal concubines.
I’m not sure if the Judge is historically correct but she is correct on the point that it should have no bearing on the law.
But, it is actually not as convincing an argument as she claims.
The form of “polygamy” that was most often practiced was singular. A man married a woman. That man married another woman, and then another woman. EACH marriage was between ONE man and ONE woman. There is little evidence of an actual marriage entered into between one man and multiple women.
What is clear is that almost no society ever applied whatever their “marriage” tradition was for the union of two people of the same sex. Marriage was intended, in both monogamous and serial polygamist forms, as the union of a man and women who could then procreate to propagate the species.
Society has no real interest in encouraging any other relationship than those which perpetuate humanity. Even if you have no care what people do with their own lives, there is no rational basis for government to take ANY interest in a relationship that has no possible benefit for humanity’s survival.
This is why we don’t mind at all if a brother and sister decide to live together, or two sisters, or even unrelated men and women, and we don’t particularly even care what they are doing, we simply don’t encourage such arrangements because they don’t give us a new generation of humans to continue our survival.