First, how can anyone know what the definition of marriage was before there was any recording of history? Does Barnes have a time machine which allows him to go back before recorded history in order to ask people before recorded history what the definition of marriage is before recorded history?

Second, it is clear that for most of recorded history, polygamy was the norm, along with plural marriage in some areas, so the history shows that "... single politician or court or legislature should attempt to redefine the very building block of our society in a way that alters its entire meaning and purpose" has been the rule, not the exception. I'm guessing that the Pope, one person, redefined marriage to outlaw polygamy, and I don't think the Pope would have accepted the demand for a vote on banning polygamy.

But then again, that's only for Catholics, while Islam with four times as many followers as the Pope says that a man can have up to four wives. Then again, that was a statement by one man to bring order to the current custom which includes some who thought many wives was good and others that thought a man should be limited to one wife.

Clearly arguing from antiquity is a logical fallacy because the logical conclusion is that the US laws prohibiting polygamy are wrong, and that the Catholic church rule of one wife is also wrong because that was a ruling by just one man.