Being Roman Catholic, my objection to the legalization of polygamy comes from Catholic teachings concerning the sanctity of marriage -
Christ affirmed and blessed the oneness and profound significance of marriage. Christian tradition, following his teaching, has always proclaimed the sanctity of marriage. It has defined marriage as the fundamental relationship in which a man and woman, by total sharing with each other, seek their own growth in holiness and that of their children, and thus show forth the presence on earth of God's kingdom.
From the Catechism of the Catholic Church (1664)
"Unity, indissolubility, and openness to fertility are essential to marriage. Polygamy is incompatible with the unity of marriage; divorce separates what God has joined together; the refusal of fertility turns married life away from its 'supreme gift,' the child."
However, this argument, when recently used against those wishing to legalize same-sex "marriage" did not win the day in New York State. Separation of Church and State and all that, we were told. When a moral argument was used to combat homosexual "marriage", we were told that, in our secularist society, civil laws could not and should not be based on religious beliefs.
While Jennifer Pizer, a law professor at the University of California, Los Angeles, assures us that the questions surrounding whether same-sex couples should be allowed to marry are significantly different from those involved in criminal prosecution of multiple marriages, her argument that the legalization of same-sex "marriage" will not produce a "parade of horribles" - where the legalization of polygamy would be the next logical step - is itself, a logically flawed argument.
There are biological arguments against same-sex "marriage" - obviously, homosexual relationships cannot produce offspring. This biological argument certainly would not apply to polygyny which, from a biological standpoint, would be the most efficient way of producing offspring. The only objections to polygyny (or the less biologically efficient polyandry) come from a moral or religious perspective. As mentioned before, those arguing for same-sex "marriage" tell us we cannot use arguments based on morality or religion.
So then, how long will it be before legal cases come before the various courts, attempting to legalize polygamy?
In a piece for reason.com, Steve Chapman tells us that anti-polygamy laws may very well violate the Constitution.
In Canada, anti-polygamy laws are also being challenged in court.
"People who practice Islam, Wicca and other religions also are adversely affected by the anti-polygamy law, Vancouver lawyers George K. Macintosh, Ludmila B. Herbst and Tim Dickson said in a brief to the court."
In May, 2008, the legal director of Lambda Legal, Jon W. Davidson called the "slippery slope argument" an "alarmist dodge". Three years later, it would appear that he was mistaken.