The government provides a contract for two people, ( normally man and women currently) to join into a civil contract in which each takes on specific liabilitys and duties toward the other. The actual terms of this contract is not national in the US, but by state, I believe even in canada the terms of the contract are by provinence and vary some.
The fallicy that this is called marriage has come from over time, the state taking over the place of the church, in early times there were no civil contracts but all marriages were arranged and tracked by the church, and in other times and cultures there were no actual legal contracts merely a custom or tradition that joined the couple with no written legal contract.
So as customs moved, and governments make laws, marriage was controled by the state , which is not the right of the governmetn to do so. So a couple can marry without a license from the state, but they do not get reconised for legal rights, this is where the state is interfering with religious culture and rights.
So does a gay couple have the right to marry, by whose standards, if they belong to a religious group that allows it, of course they can but that does not mean a governemnt has to reconinse it. That is a different standard.
The laws of a government is set by the culture and moral fiber of its citizens, in such the nature in the US today is that such marriages are not to be allowed, and as such the laws of the nation should reflect that if the government is going to control it. ( which it should not)
Should a religious body be free to refuse to perform a gay marriage of course, and in some areas where religous groups are being forced to have to reconise these, that is another abuse of state power.
So the nation as a law should not even be issuing marriage.
As for me personally, no gay marriage is against the moral laws of God, against nature and is disgrace of how low man can move down the ladder of evolution.