Most cultures? Really? Well, we live in the Western World, so really in order to compare, you should compare us to other Western nations. Name one Western society (not cult) that supports polygamy? I realize some African and Middle Eastern cultures do have polygamy, but they also have other 'customs' that we would find very abhorrent. Stoning of a woman for alleged adultery, the raping of children to 'cure AIDS', the list goes on. Shall we base our laws/beliefs on what is 'normal' in cultures we share little in common with?
Further, most polygamist 'marriages' in North America are of the Fundamentalist Mormon variety (ie, Bountiful BC, Utah, etc.). It is debatable whether this is consentual or not. There is immense pressure on the young women (or children) in these communes to marry much older men who already have 1 or more wives. IIRC, they beleive that men may enter heaven only if they have 7 wives. Again, if you feel that this C-48 will lead to legalized polygamy, then you should be informed on what it actually is. Whether it actually will lead to it is a whole other matter, and certainly up for debate.