Gay marriage is not a fundamental civil right.
I am not a Christian, and I have no problem with gay people. One of my best friends is gay.
But since when has marriage between people of the same sex been considered a "fundamental civil right"?
Answer: Since gay people decided it would be a shortcut to "acceptance"--just get the law to SAY it's so, and wheee! Everyone will accept gay people as equals.
It's a lazy, embarrassingly dishonest attempt twisting reality to fit a model that has never, ever existed in any society.
If two adults of whatever sex want to live together there's nothing stopping them from doing so. No law restricts who can and cannot be named as a beneficiary in a Will. And Power of Attorney may freely be granted and revoked between consenting adults.
The legal foundations of marriage are based upon society's interest in the protection of any children which may issue from that marriage, for by definition they represent the future of that society. The state has no say in the religious dimensions of marriage (and in the U.S. that prohibition is explicit in the 1st Amendment) other than to note that such foundations exist and are part of every faith and creed.