The heart of Meachem’s argument does not bear much scrutiny, and we have not even come to the question of how entirely divorced Meachem’s entire argument is from a Christian understanding of the purpose of marriage. Procreation is an important part of that purpose, and joining two people from different sexes in complementary relationship is another, but beyond that it is a vocation to unite oneself to a person radically different from oneself. The uniting of complementary opposites as a type of the unity between Christ and His Church is one of the mystical meanings of marriage. The Christian conception of marriage is of two people joined into one flesh, the full expression of which is a child. Nowhere in the “great Judeo-Christian tradition” that Meachem supposedly takes so seriously is there support for his argument.So you see, on a theological basis this will never, ever be resolved. It simply won't. The Bible forbids homosexuality, eating pork, masturbation, and hundreds of other outdated things, and people will focus on that and on the notion that marriage is solely for procreation (the logical conclusion being we should not be allowed to marry even if we are straight if we don't plan on having kids) and not on the more compelling Biblical truths like love and redemption and sacrifice and holiness.
So give marriage over to the Churches, universalize civil unions, and be done with it.