Oh, those awful patriarchs and kings. How could they have been so wrong? And their wives, their FIRST wives, their REAL wives--how could they stand it? Why did they stand it?
"Lamech took to himself two wives: the name of the one was Adah, and the name of the other, Zillah" (Gen 4:19). This is the first we hear of polygamy in the Bible. If one wife is good, two must be better; and Lamech's reasoning is found amenable for generations thereafter.
Interesting that God does not provide any editorial remark. Doesn't He think polygamy is bad? Well, yes. It's terrible. So terrible no one needs to say it's bad because every sane person knows. God also makes no comment on Lamech's bragging on his own malice and bloodlust a few verses down. We don't need to have it spelled out for us that Lamech's sins are sins.
But anyway, imagine Lamech's kids and neighbors. Meh, two wives. That's just how we do it in our tent, just how they do it next door. Not normal for everybody, but normal for Lamech. And what's normal for your dad or your neighbor, well, it's not that weird, right? Something you see every day isn't weird. Normal for Lamech and Adah and Zillah becomes normal for their sons, normal for their daughters, normal for their neighbors, just normal.
So Jacob: another week, another wife. David, a man after God's own heart, never gives us an indication that this polygamy business keeps him up at night for any good reason (neither does the practice solve his lust problem). Even tender Elkanah cannot imagine himself to be worth less to Hannah than ten sons, oblivious to having given her only half of himself. And if our main concern is that polygamy is bad for women, I wonder if 1000 lonely Ancient Near East guys might have some insights to offer wise Solomon.
What happens to polygamy? Exile, probably, and the poverty it brings. Roman occupation and law (thanks for that at least, nations). Once polygamy becomes abnormal again, its wrongness becomes self-evident to Christians. (Though our honored fathers can still trip us up.)
Polygamy: the sexual sin the people of God--good, pious, exemplary people of God--could not live without. Fornication, divorce and prostitution/pornography being roughly historically equal, can we possibly be so arrogant as to imagine that we have transcended this capacity for tremendous transgression, for unthinkable unchastity?
But don't worry, Protestants. As long as you're not a bishop (and what Protestant would be?) the Bible doesn't say you can't have two wives. As my favorite pastor told me, "At least polygamy is life-affirming."