Here are the Ten Commandments:
1 You shall have no other gods before Me.
2 You shall not make idols.
3 You shall not take the name of the LORD your God in vain.
4 Remember the Sabbath day, to keep it holy.
5 Honor your father and your mother.
6 You shall not murder.
7 You shall not commit adultery.
8 You shall not steal.
9 You shall not bear false witness against your neighbor.
10 You shall not covet.
We have never tried to encode in the Constitution Commandments 1, 2, 3, 5, and 10.
Attempts to encode 4 have largely failed. Jews and Adventists celebrate the Sabbath on Saturday, Christians on Sunday, Muslims on Friday. There have been Blue Laws against stores selling stuff on Sunday, but about all that is left of this are laws against selling booze before noon.
Adultery is one of several grounds for divorce, but is not penalized otherwise.
Perjury, lying under oath, is penalized, as is fraud and libel to some degree.
So of the Ten Commandments, we no longer enforce over half. Marriage is not mentioned in the Ten Commandments. Neither is abortion or gun control.
Although morality is connected to religions, civil morality is now and always had been a matter for legislation rather than religion. Being as we have a lot of religions in the US, and none of them is in any way official, I do not see how recognizing gay marriage affects anyone but gay people.
I have no objections to Steve or Eve marrying Airedales, but I imagine that ridicule would be the main social constraint against it. I am against people claiming their pets as dependents on their income taxes. Imagine what claiming all the ants in one's ant farm as dependents could do to a Form 1040.
Most religions are based on a fairly obvious premise that humans are the moral center of the Universe and the justification for its existence and the epitome of its existence. We are some sort of special hobby of God's, and were created as sort of special pets, and occupy the center of Creation.
Any astronomer can tell you that we are not at the Center of anything. We are land creatures who dwell on a rather small planet most covered by water located on a trailing arm of a rather ordinary galaxy. An infinite Universe can have no center, and it is likely that there is more than one infinite Universe.
We seem to have invented religions to give a sense of order to our existence as well as to inflate our egos. That does not mean that God does not exist or does exist. The odds that most of the beliefs of most religions, however, such as virgin birth, miracles, a finite series of prophets, the divine endorsement of The Ark of the Covenant, the Koran, Bible, Book of Mormon, are against any of these and similar things being part of the structure of the Earth or the Universe.