I know that in some corners of conservative Christianity, that's the rhetorical argument du jour against the Supreme Court's legalization of gay marriage nationally last week. (That's if they've not already stooped to the ridiculous and claim bestiality or child marriage is next.)
First, especially for conservative Christians who always like that "Judeo" fig leaf on "Judeo-Christian values," er, your past religious heritage shoots you in the foot.
Many of the "heroes" of the Christian Old Testament/Jewish Tanakh had multiple wives. (Yes, technically that's polygyny, not polygamy, which cuts both ways and could also include multiple gay or lesbian marriages at once, but, usually, polygamy winds up as one man and several wives. So, we use polygamy throughout.)
But, Jesus said!
Erm, no he didn't, and claims that his comments disallowing divorce prove either that he was anti-polygamy or that polygamy no longer existed at his time simply aren't true. The actual Paul may have been anti-polygamy, and the pseudo-Paul who wrote the Pastoral Letters certainly was, but that's a different story.
However, while Greeks and Romans were one-spouse folks (not counting mistresses, of course), some sects of Judaism still allowed polygamy at the time of the New Testament.
As for today? There's religious freedom grounds for it, primarily for Islam, but also for the Fundamentalist LDS. And, while Ashkenazi have officially banned it for a millennium, Sephardi still accept it, and Orthodox among them still argue for it today. And, to really screw with fundy Christians, a "Messianic Jewish" rabbi practices it in London. And, although legally banned, it's also practiced in Israel.
So, why shouldn't polygamy be legally protected? Fredrick de Boer offers an in-depth argument in support.
I agree. First, per my comment about mistresses, he says polyamory's been around as long as the "nuclear family." Beyond "mistresses," polyamory as all multiple relationships, none of them "legalized" by marriage, has been gaining steam.
Second, the legalization of same-sex marriage has refuted the old "for having kids" argument. Of course, older straights getting married has always been Argument No. 1 against that.
deBoer then notes that traditional marriages, like polygamous ones, can be havens of abuse. Duggar Family Values, anybody?
I would go beyond deBoer, at least what he explicitly mentions.
I would require a man or a woman wanting to enter a second or additional marriage to publicly disclose he's married to another person already. As it already generally is considered with no polygamy today, such failure to disclose would be legally considered fraud — and should be considered felony-level fraud
For commenters or others who think this is "snark," it's not.
To go beyond my comment response to Joshuaism, most of the comment is red herring.
First, consent is "manufactured" in single marriages. Don't tell me you haven't heard of Indian-Americans still marrying the spouses their parents have arranged for them.
Second, the consent issue has nothing to do with incest, which I'll tackle separately.
Third, to elaborate on my comment about Macedo's Slate article, of course there can be one-to-one meeting on each marital partner in a plural marriage. Maybe there can't be one-to-one 100 percent meeting, but if you're expecting that, then you've got a definitely naive, possibly harmful "absolute soulmate" view of marriage in general. No marital partner should be, or should be expected to be, the 100 percent match, complement, "meeting" or whatever of another marital partner.
This expands on what I noted was of concern in Kennedy's ruling — the over-uplifting of marriage as more than it really is, or really should be expected to be.
For both him and possibly Katy, beyond the public health angle, I think the state can make a plausible, even compelling, public mental health angle against incestuous marriage. While questioning the over-uplifting of marriage, I don't want to over-devaluate it, either. And, yes, especially with kids, the whole wrecking of the normal plot of extended family relations that an incestuous marriage would cause would be a public mental health concern.