The problem is that too many people either no longer accept this historical view of marriage, or they don't wish to "impose" their view on others (for fear of being called a bigot), or they have a "live and let live" philosophy that has opened the door to virtually any and every experiment in social arrangement. If same-sex marriage is allowed, it is going to be nearly impossible to prohibit the sanctioning of any other kind of human "relationship" - from close relatives of different sexes who wish to marry (that has been outlawed because of biological and incest considerations) and polygamists to adult-child "marriage."
I recently asked Republican New York Gov. George Pataki if he favored same-sex marriage. He said he doesn't but thinks some accommodation could be made to homosexuals offering similar benefits. What about polygamy? He quickly rejected that, saying "it is against the law." The New Paltz mayor is violating the law, but New York's Attorney General won't stop him. If things that are illegal violate cultural trendiness, our new definition of "truth," they are simply permitted.
I don't know how you reverse such a trend. Political activism isn't working. Appeals to higher standards aren't successful, because same-sex "marriage" is evidence that the standards have already been abandoned. How does a nation that has tolerated about 40 million abortions suddenly acquire a moral sense about same-sex marriage?
Maybe those of us wishing to preserve marriage for heterosexuals, imperfect as we may be at it, ought to ask those pushing for its redefinition what they mean by their "fairness doctrine" and upon what it is based. At least we heterosexuals have a reference that is thousands of years old. What's theirs and how do we know it won't change tomorrow?