Whether by customary or written law, almost every human culture has rules regarding marriage between heterosexual couples. Mankind has long understood the importance of monogamy and the protection of the children from that relationship. You can go to the darkest depths of the Amazon and you will find "customary" rules being enforced. Partly, these "rules" are "understood" to keep order in the community by stifling fights over spouses. But, more than anything, these rules are in effect to protect the children.
In our modern culture, the laws regarding marriage are generally designed to protect the woman with children from desertion by the husband. The assumption has always been the the burden of taking care of any offspring makes it prohibitive for a mother with children to work outside of the home. In fact, a married woman working outside of the home environment is a modern occurrence; and, many of the marriage laws existed long before this advent.
When we, as a modern society, decided to allow gay and lesbian couples to adopt children, we, by default, called into effect the laws involving marriage; whether we like it or not. It has nothing to do with religion. As I said before, the unwritten laws of marriage existed long before any formal and broad-based religions ever came to be.
It is all about the children and the potential of having children in any kind relationship; whether homosexual or heterosexual. It isn't about furthering the acceptance of gays in our society. We've gone well beyond that. Now its down to protecting a relationship so that the weaker of that relationship, the children, that are generally protected under our laws. While this is abhorrent to my personal and religious beliefs and to the many religions in the world, logic overrides that disdain. If organized religions want to protect the "word" marriage, that's fine. All marriages, heterosexual or gay, can be certified as "unions" under the law and "marriage" under religion. After all, "marriage" in religious terms is a morally binding "state" that is a relationship between a man and a woman; before God. It is only the "state" that certifies marriage by issuing a legally binding license.
All the efforts to block gay unions is simply avoiding the inevitable. It is a futile effort and we should all get over it. While the whole "gay thing" is still an emotional issue with me and most heterosexual people, I think I am finally OK, on a logical basis, with the concept of gay marriage or gay unions.