It really depresses me sometimes to think people refuse to accept some beliefs and are okay with others... I know this is a little off topic but Deanna and I were talking the other day and I came to the realization about how stupid refusing gay marriage is. Most are apposed to the idea because it is supposed to be a holy marriage between man and woman, right? They bring God into the equation all the time and yet Atheist get married all the time. They are fine with this. It makes no sense to me at all. Everyone should be able to get married, not just a select few.
I don't believe that's a fair characterization of the argument. For instance, the opposition of the Catholic Church to same-sex marriage is based on the premise that sex is meaningful only when it is both unitive and procreative. The purpose of marriage is to instutionalize the norms that govern the creation of human life. Marriage is not recognized for its own sake or for the sake of the two partners, but for the life-generating capacity of the union. Indeed, there are many loving relationships of equal or greater value to society than a bare sexual or mutually supportive relationship (like siblings or friends); the reason that committed heterosexual sexual relationships are given special legal recognition is because it is a symbol which conveys respect for the natural transmission of human life. To the extent that the Roman Catholic position is based on a belief in God, it is primarily as authority for the proposition that a committed and loving relationship is the ideal environment for the creation of life.
Marriages between heterosexual atheists do not jeopardize that basic premise; marriages between homosexuals do since, once permitted, it is impossible to say that marriage is about recognizing the importance of the procreative capacity of sexual relationships. By recognizing same-sex unions as capable of marriage, marriage becomes a simple status symbol of unity and love between two individuals - it is no longer related to the norms and environment in which the society wishes its citizens to be created. Absent that function, there is indeed no institution in society which conveys any particular respect for natural procreation and sexual relationships are valued only for their unitive purposes.
That said, that argument has more consistency within the Catholic Church than in the broader society since that is the same reason that artificial contraception is banned, masturbation is intrinsically disordered, and infertility is a ground for annulment. In the broader society, there is nothing preventing infertile couples from marrying or married couples from choosing not to have sex which is open to procreation. Same-sex marriage still jeopardizes marriage as a symbol of procreation, but whether that symbol has any remaining normative force is uncertain.
That said, there are opponents of same-sex marriage whose views are less consistent and perhaps based primarily out of prejuice, including some Catholics and other Christians. However, I don't think the
official position of the Catholic Church or of those who espouse it are among those.
Obviously, that is just one example of one sect of one religion, but my point is that I disagree with your characterization of the religious interest in opposing same-sex marriage. I don't believe same-sex marriage is a matter of justice where all opponents to it are irrational or immoral or out-dated; I think it is simply a dispute between competing values and visions for the role of marriage within society.