Polygamy meant that a wealthy man could have multiple wives. These wives and their offspring ate better, got better medical care, had better clothing, than the wife & kids of some poor subsistence farmer scratching out a living on a tiny plot of rocky land.
Of course, this left many lower scale men unable to find mates at all. But the excess males were put to work building pyramids, rowing ships, fighting wars, and so forth.
Polygamy clearly does not fit into a society where people on the whole are well off, and where concepts of human liberty are important. Ditto for slavery. Many people project backwards on these issues and react with horror that the Greeks owned slaves. But slavery basically served the function of a social program, providing the rich with an incentive to care for at least some of the poor. If you owned a slave, it was in your best interest to feed him and keep him healthy.
This is why neither slavery nor polygamy are outright condemned in the Bible. But neither are they mandated. As our societies grew wealthier and as our understanding of human liberty grew stronger, we discarded these institutions as inappropriate for our Western Civilization. The fact that liberals are now talking about bringing polygamy back shows they have no historical understanding whatsoever, and are merely trying to destroy us and make life easier for our sworn enemy Islam. They'd bring back slavery, too, if they had a chance.
BTW, I should have added that same-sex “marriage” is of no value whatsoever in any society, and is always destructive of the social order. This is why homosexual acts are thoroughly condemned in the Bible.
Under these circumstances, and with the state of the law as announced in Lawrence and Goodridge, legalized polygamy is inevitable, and will come sooner than you think.