Motherbear and I oppose legal polygamy in America because it would hurt our children and our children's children. We and others like us will use the processes of democracy to preserve the decencies we love and to suppress the social forces of dissolution.
None but tyrants would impose legal polygamy on a society that overwhelmingly opposes it. Of course, as we see, there is no shortage of tyrants.
Fashioning "a decent society" is certainly a matter of moral perspective, and one we probably agree on morality-wise. I don't want my kids hanging out in Hugh Hefner's neighborhood because kids are not ready for adult behavior or the consequences thereof. That's why parents keep an eye on their kids, to help them know what to do when they are ready to judge for themselves.
On the other hand, I don't feel I should have any say on what Hugh does in his home, or what my kids do after they leave my home. Obviously, you disagree and think it's important to regulate what people do in and outside of their homes insofar as the legal status of their spouse is concerned. Never mind that the only difference in the legal status is who can be a current WIFE, not current floozy, so your 'upholding decency' argument really holds no water. What you want is to uphold your version of morality in LAW, never mind the actual negative social consequences of that illegality or its inability to effect any positive change towards your perception of good. You prefer the spirit of the law to its reality. And what you consider a factor in 'dissolution' has been a part of many stable societies for hundreds of years. People weren't rioting in Utah before polygamy was banned there, either.
I doubt you would be making that 'none but tyrants' speech if King George or Congress imposed a BAN on gay civil unions, which arguably have the support of a majority in the U.S. So your demagoguery about tyranny falls flat. You USE the processes of democracy--but you don't believe in that institution, and if you had your way, there would be a tyranny of the righteous, whatever your definition of that is. I don't think any judge should make the law here either, ma'am, but if they did, it would be expanding people's freedom to associate as they see fit, not restricting it. And expanding freedom is rarely a bad thing.