This semester, I am enrolled in a course in Family Law. Two weeks ago, we had an extensive discussion about polygamy (particularly in the FLDS context) and I became quite involved in it. A classmate of mine pointed out that too frequently, polygamy is immediately associated with Mormonism, while it is also practiced widely by neopagans (Wicca, etc.) and Muslims (though not in the US). I was thankful to him for that point, not only in recognizing that polygamy is not exclusively a Mormon "problem" but also for the fact that I was no longer the person in the room with the weirdest religion (he had previously confessed that he himself was a neo-pagan).
The reason I mention all this is that it got me thinking about how anger and ridicule over polygamy gets rolled into general anti-Mormonism. Anti-Mormonism did not begin with Joseph's practice of polygamy. The JS-H attests to this; but also there is some argument that Joseph's polygamous wives were not publicly known before his martyrdom, which was a direct result of anti-Mormonism. However, it is likewise indisputable that a large portion of anti-Mormonism in the late 19th and 20th centuries, even up until know, is based in the Church's previous practice of polygamy and the mistaken impression that it is still practiced among us. My impression is that the two (the larger anti-Mormon sentiment and the horror of polygamy) feed off of one another. If polygamy were no longer an issue, anti-Mormons would focus on something else. But many people who might be willing to let Mormons alone on many theological differences get very riled up about the Church's practice of polygamy.
I say this as someone who supports the 1st Amendment rights of polygamists to practice their religious beliefs. I understand that polygamy (particularly as practiced by FLDS) has many attendant evils, e.g. the "Lost Boys", sexual abuse, incest, etc. However, a blanket prohibition on polygamy is too blunt an instrument to deal with these issues. Nor would I be against polygamists who entered into plural marriage for purely secular reasons or simply as a matter of preference. I do not say this as a Mormon, and therefore predisposed to sympathize with polygamists, or as a liberal, and similarly predisposed to allow plurality of belief (and some would say sexual freedom). Rather I think the liberty-related imperatives of our Constitution show that previous laws or decisions that would prohibit polygamy were profoundly mistaken and un-American.