The will of the majority has already been rejected. That's the point. The Massachusetts ruling demolished the reasoning that marriage is based on what the majority wants.
A majority of Americans abhor same-sex unions, yet the courts found their opinion moot. A person therefore cannot appeal to “what the people want” in arguing against polygamy.
It no longer matters how many individuals advocate polygamy (though it is more than just a few; there are an estimated 20,000 - 30,000 practicing non-legal plural marriage in Utah alone). What matters is the soundness of their argument presented in court.
Using the precedent made in Lawrence v. Texas, polygamists have the upper hand in the debate. Their argument will be even more unstoppable, if the Supreme Court upholds the Massachusetts gay marriage ruling. That ruling, incidentally, citing Lawrence v. Texas as the basis.
The only way to prevent them from succeeding is the Federal Marriage Amendment. That is why polygamists opposed it.
If you're referring to the FMA, all the surveys I've seen indicated an unwillingness to amend the Constitution that correspond roughly to today's actual vote. It doesn't necessarily mean acceptance of gay marriage, there will be some tests this fall of that.
The Massachusetts ruling demolished the reasoning that marriage is based on what the majority wants.
Did the MA SJC turn things on their head? Perhaps, I really believed that it surprised even the gay rights people. If it had not occurred, we would not have seen the rouge marriage licenses in SF, Portland, New Paltz, etc. Those incidents may well have been overreaching by the gay rights side. It seemed to me that their strategy was to get civil union or domestic partnership in as many places as possible, then use a "separate but unequal" argument in the courts. Gay marriage advocates are quite full of themselves right now, and anything they can use as a "victory" will keep them giddy. I think Senator Frist's vote just provided such an opportunity.
A majority of Americans abhor same-sex unions, yet the courts found their opinion moot.
Of course, it depends on where you ask the question, but most surveys I've seen are about 30% in favor of full gay marriage, 40% dead set against anything, and a mushy middle of about 30% either in favor of civil unions, or not really caring about the issue. That 30% is what both of the other sides are fighting over, and by no means is the 40% going to win them all over, in the long run.
What matters is the soundness of their argument presented in court.
It would take a LOT to convince a Utah appeals court of the application of Lawrence vs. Texas to the condition of polygamy. Every Mormon I've ever known has been paranoid about discussing it, they're sick and tired of all the jokes. Surely, LDS-approved appeals justices in Utah will strike this "reasoning" down. This lawyer picked too hard a target. He might have had better luck in Maine!
That is why polygamists opposed it.
The polygamists are a tiny fringe group that really does want to radically redefine marriage in America, and they will cling to anything that they see gives them legitimacy. Find me a so-called "Biblical" polygamist who really thinks that Leviticus and Paul are all wet on homosexuality, and I'll find you the biggest hypocrite in the country!