Argument: Gay marriage is slippery slope to polygamous marriage etc.
Adam Kolasinksi. "The Secular Case Against Gay Marriage." The Tech (M.I.T.). February 20th, 2004: "The biggest danger homosexual civil marriage presents is the enshrining into law the notion that sexual love, regardless of its fecundity, is the sole criterion for marriage. If the state must recognize a marriage of two men simply because they love one another, upon what basis cant it deny marital recognition to a group of two men and three women, for example, or a sterile brother and sister who claim to love each other? Homosexual activists protest that they only want all couples treated equally. But why is sexual love between two people more worthy of state sanction that love between three, or five? When the purpose of marriage is procreation, the answer is obvious. If sexual love becomes the primary purpose, the restriction of marriage to couples loses its logical basis, leading to marital chaos."
Stanly Kurtz. "Beyond Gay Marriage." The Weekly Standard. August 4th, 2003: "If gays had a right to marry, why not polygamists?... Marriage will be transformed into a variety of relationship contracts, linking two, three, or more individuals (however weakly and temporarily) in every conceivable combination of male and female. A scare scenario? Hardly. The bottom of this slope is visible from where we stand. Advocacy of legalized polygamy is growing. A network of grass-roots organizations seeking legal recognition for group marriage already exists. The cause of legalized group marriage is championed by a powerful faction of family law specialists. Influential legal bodies in both the United States and Canada have presented radical programs of marital reform. Some of these quasi-governmental proposals go so far as to suggest the abolition of marriage. The ideas behind this movement have already achieved surprising influence with a prominent American politician...The [Tom] Green trial in 2001 was not just a cable spectacle. It brought out a surprising number of mainstream defenses of polygamy. And most of the defenders went to bat for polygamy by drawing direct comparisons to gay marriage...Writing in the Village Voice, gay leftist Richard Goldstein equated the drive for state-sanctioned polygamy with the movement for gay marriage. The political reluctance of gays to embrace polygamists was understandable, said Goldstein, but our fates are entwined in fundamental ways....Syndicated liberal columnist Ellen Goodman took up the cause of polygamy with a direct comparison to gay marriage...Stephen Clark, the legal director of the Utah ACLU, has said, 'Talking to Utah's polygamists is like talking to gays and lesbians who really want the right to live their lives.'"
Alliance Defense Fund on Opposing Views.com. Retrieved 3.1.2010: "Those who agitate to de-define marriage consistently ignore the reason the state recognizes marriage in the first place. In America, marriage has always been an institution existing primarily to protect children created within the one and only union that can naturally produce children. The opposition has twisted marriage into a government endorsement of close relationships. The logical end of that idea is obvious: there no longer exists a legal difference between same-sex couples who want to “marry” and all other combinations of “loving” adults who want to “marry the person (or people) of their choice.” If marriage is nothing but a state stamp of approval on intimate adult relationships, what is the argument for denying “marriage” to any number or combination of adults who claim to be “in love”? If the gender composition of a marriage is unimportant, what is so sacred about the number of participants? The very arguments used on behalf of same-sex couples apply equally to “bisexuals” or polyamorists who would like to “marry” a number of different people.
What about a brother and sister “in love?” The typical objection when confronted with the brother-sister “marriage” challenge is that procreation between siblings increases the chance for birth defects in children. So then, what is the objection to two brothers “marrying?” The opposition cannot object to a brother-brother “marriage” absent an appeal to a moral standard. But in objecting to all sibling “marriages” they are unwittingly arguing that marriage: 1) is essentially a procreative institution, 2) benefits the state primarily as a child-protective institution, and 3) may be limited by moral considerations. These are the very arguments they must reject in order to justify the imposition of same-sex “marriage.” But the opposition refuses to engage in a thoughtful debate on these issues. They know, when confronted with their own self-negating logic, their slippery slope becomes a steep cliff. If marriage can mean same-sex relationships, it can mean anything. If marriage can mean anything, it means nothing. If marriage means nothing, children are guaranteed to pay the price."