It was landmark U.S. Supreme Court precedent
Reynolds v. United States in 1878 that made “separation of church and state” a
dubiously legitimate point of case law, but more importantly;
it confirmed the Constitutionality in statutory regulation of marriage practices.“Laws are made for the government of actions, and while they cannot interfere with mere religious belief and opinions, they may with practices...” Reynolds v. United States, 98 U.S. 145, 8 Otto 145, 24 L. Ed. 244 (1878).
[See also: Late Corporation of the Church of Jesus Christ of Latter-Day Saints v. United States, 136 U.S. 1, 10 S.Ct. 792, 34 L. Ed. 478 (1890). Revised as 140 U.S. 665, 11 S.Ct. 884, 35 L. Ed. 592 (1891).]
Congress, state legislatures and public referenda have statutorily determined polygamous, pederast, homosexual, and incestuous marriages are unlawful. No Constitutional Amendment restricting marriage is required to regulate "practice" according to the Reynolds decision.
Marriage is a religious “rite,” not a civil “right;” a secular standard of human reproductive biology united with the Judaic Adam and Eve model of monogamy in creationist belief. Two homosexuals cannot be "monogamous" because the word denotes a biological procreation they are not capable of together; human reproductive biology is an obvious secular standard.
All adults have privilege to marry one consenting adult of opposite gender; therefore, Fourteenth Amendment “equal protection” argument about "privileges and immunities" for homosexual marriage is invalid.
Driving, marriage, legal and medical practices are not enumerated rights; they are privileged practices that require statutory license. Nothing that requires a license is a right.
Homosexual monogamy advocates are a cult of perversion seeking ceremonious sanctification for voluntary deviancy with anatomical function and are desperately pursuing esoteric absolution to justify their guilt-ridden egos. This has no secular standard; it is an idolatrous fetish.
"Homosexual monogamy advocates are a cult of perversion seeking ceremonious sanctification for voluntary deviancy with anatomical function and are desperately pursuing esoteric absolution to justify their guilt-ridden egos. This has no secular standard; it is an idolatrous fetish." 
That's not really my focus or point.
I'm looking at a larger picture. I don't like *government* performing religious rites (e.g. baptism, bar mitzvahs, marriages, etc.).
I'm uncomfortable with government involvement in church ceremonies, church rites, religious doctrine, etc.
I should be able to argue my religious preferences inside my church. I should not have to make those arguments to my government for public policy.
I don't even want government passing a "blue law" that says that churches or businesses can't be open on Sunday.
Basically, I want government out of religion.
Government itself shouldn't "sanctify" or justify or approve or ban any aspect of any religious ceremony/rite...although I can accept government banning certain practices such as ritual human sacrifice for Satanists.
But more realistically, government should be blind to religious status. Government shouldn't ask me if I'm circumcized and government shouldn't ask me if I'm baptized or married.
Government should have no opinion on such things. Those are the domain of religion.