Traditional Marriage was never Traditional

The defenders of traditional marriage are not defending traditional marriage—they are defending their own unique religious version of marriage which is that marriage is a "God-ordained" institution that is between one man and one woman and has been so for all of history. By "God-ordained" they mean the Christian God. The alleged gods of other faiths don't matter.

History is filled with accounts of polygamy. The Bible claims that polygamy was common with people like Esau having two wives; Abraham was married to Sarah and Hagar; David had multiple wives and concubines both, as did Solomon. Marriage has not always been about one man and one woman.  

 

Christians claim marriage has always been between individuals of the opposite sex.

Remember the Christian emperor of Rome, Theodosius II, well he created a code of Christian law for the Roman Empire which specifically banned same-sex marriage. Why ban something that was never practiced?

How about the claim that the collapse of Rome came about because it tolerated homosexuality? Rome under Christian rule became more intolerant of homosexuality long before it collapsed. The banning of same-sex marriage was the first step of a series of anti-gay laws. Rome was tolerant of gays during its height and least tolerant before its collapse. Christians were tolerated and ruled Rome during the fall of the empire.

Many claim that marriage was a "divine institution" all along and that the state took control of marriage from the church.

Marriage was neither connected to the church or to the state for much of history. A marriage amounted to two individuals announcing their marriage to friends and family and setting up house. There may have been a "wedding feast" as depicted in the New Testament but there was no church ceremony. Early Christian churches had nothing to do with marriage. They did not perform marriages.

Marriage was considered valid if two individuals merely pledged themselves to one another, regardless if anyone else knew about the matter. Martin Luther wrote marriage was "of the earthly kingdom" and "subject to the prince, not to the Pope."

The state did not take over marriage. First, marriage was entirely private without interference of either church or state. Catholicism exerted control over marriage in 1545. It was the Protestant Reformations that brought in state control of marriage. Protestant leaders invited the state to take control of marriage. John Calvin's 1545 "Marriage Ordinance of Geneva" required a state permit and church consecration before a marriage was recognized. Of course they thought they had control of the state.