That's utter nonsense.
The Catholic Church began requiring banns of marriage in the early 13th century, it was done in many areas even before this. Banns were explicitly kept as a requirement by Protestants during the reformation.
So, I would hardly call eight hundred years "relatively modern" as it predates nearly all other forms of English Common Law on which American laws were based.
Moreover, prior to VERY RECENTLY, NOBODY would have ever thought to define marriage as anything other than between a man and woman. Even cultures that practiced polygamy never defined marriage as between two members of the same gender.
The whole "government shouldn't be involved in marriage licensing" is simply the latest libertarian attempt to support the left's agenda while pretending not to.
Ok, the Catholic church was the government.
I have no problem with churches defining marriage, I have a problem with governments defining marriage.
If the government can define it as between one man and one woman, they are then permitted to define it as anything they want.
The civil union part needs to be separated from the spiritual part called marriage.
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Exactly right.