However, there is another much more basic point that opponents of gay marriage intentionally miss. Religious marriage is not being redefined for the basic reason that state legislatures never define what a particular church believes. We don't hold a vote and tell the Vatican what they think. Democracy is not a strong point in many religious traditions. Nobody is redefining the kind of marriage that these loud-mouths care about, which is religious marriage.
They were only ever talking about legal marriage, which has long been completely separate from what you do at a church. You don't get your marriage licensed issued by a church. It is issued by the state. You can then choose to get married by any person licensed to perform marriage, which includes religious people and non-religious people alike.
The definition of legal, state-established marriage gets changed all the time, depending upon where you are. The age at which you get married, requirements for genetic testing, etc are all things that vary from time to time and place to place.
When people talk about "God's marriage" that is not something that any state legislature claimed it would or could change. As I've already said, the New York State Senate only passes laws relating to their state. Nowhere do they claim to vote about, or care about, the various definitions that your church may have relating to theological doctrines.
Many churches do not even recognize the marriages of those outside the faith. Therefore gay marriage is simply one more thing for them to not recognize.
The fact that religious people are confused on this point proves that their religious traditions have been, for too long, injecting themselves into state matters where they don't belong. Marriage is one of the last remaining vestiges of a time when religion used to co-mingle with the state, and it is high time that we insisted on the clearest possible division between the two.