The premise of the article is that marriage, in addition to being the union between a man and a woman, is two other things that have largely been forgotten today: procreative and indissoluble. Because the church has forgotten these things--that marriage is life-long and that it ought to be fruitful--and has instead allowed couples to marry who hold onto the option of divorce (even if looked at diaspprovingly) and who use contraception so as to avoid God's gift of life through their one-flesh union, she has already lost the debate on same-sex "marriage."
If Christian couples can separate marriage from having children, there is no socially defensible reason to exclude same-sex couples from having a culturally recognized marriage.
Is the Church willing to say that divorce is just as sinful as adultery or that contraception is as sinful as divorce? Is she willing to admit that divorce and cohabitation are cut from the same cloth, just as contraception and and abortion hail from the same anti-birth, anti-child mindset?
The article concludes:
If we are truly to defend marriage in this country, and not the contractual couplehood that has for some time now been disguising itself as “marriage,” then it is imperative for us to recover the full meaning of that beautiful covenant whose embodiment is now clandestine and highly countercultural. This will, I think, have to be done from the ground up, and it will take generations to succeed, if in fact it succeeds at all. It will have to be lived out first in small communities that embrace and support the self-giving, procreative, and indissoluble nature of that union, and who do so not as an unjustifiable exclusion, but as a positive commitment to protect such an important, difficult, and beautiful undertaking.
Don't take my word for it, go read the whole thing.