I see absolutely nothing wrong with polygamous marriage. It makes no difference to me if a man or woman wants multiple wives/husbands, assuming of course that everyone involved is a consenting adult. And yet polygamy is illegal in the US and most other Western countries as far as I know. I see no reasonable basis for polygamy to be illegal. I see it in the same vein as sodomy laws and laws “defining” marriage to exclude same-gender marriage. It has nothing to do with reason and everything to do with the Christian notion of sin.
And yet, even among my open-minded, liberal, atheist/agnostic friends, I find a great deal of opposition to plural marriage. I don’t get it, and I’ve never been able to glean a more incisive argument than “uh, it’s just wrong.” Perhaps you enlightened souls can educate me. Why is plural marriage immoral?