The fact is, most people in our culture who are no longer practicing Christians (or Jews) have nonetheless internalized the principles that define the way of life that has made us so successful. Many of us (for I am one of these) truly extol devotion to marriage and family without understanding the word "sacrament."
The opposition knows that, due to the fading influence of the church, we are now dealing with a "softer" form of tradition. It has been removed from theology, and they argue (and believe) that devotion to marriage and family is just as available to gay couples.
But from a purely cold, calculated public policy perspective, it is nonsense. How many gay couples are going to produce healthy booming families, that pass their family-producing practices down through generations? Almost none. So all that remains is that they are selfish. They want what others have. Well, the government doesn't exist to protect the feelings of those who are different. It exists, in great part, to preserve institutions like the rule of law. "Gay marriage" is only a distraction from this purpose.
One of them said "if two people love each other they should be allowed to get married" and I said "what if I love two men and want to marry both of them, by your definition, you'd be discriminating against me if you didn't allow me to marry them both" - all of them thought I was nuts and that situation would never happen. None of them were aware that there is a couple of cases of polygamists waiting before the supreme court... and looking to us here in Mass to see how our situation ends up.
All in all, I was distressed and realized (as does my husband) that civil unions will indeed probably go through in March.