Since I was the one who posted in Ask JTF about polygamy, I figured I'd throw my two cents in here, being that I strongly disagree with Chaim on this, and I apologize in advance for my long post. As I see it, even though polygamy was not prohibited, it was not directly sanctioned either.
First off Genesis says the following:
Therefore shall a man leave his father and his mother, and shall cleave unto his wife, and they shall be one flesh.
Notice that Genesis did not say "wives." Also, once you marry one wife, how can you leave your mother and father a second time?
And consider Deuteronomy 17:14-17
14 When you enter the land the LORD your God is giving you and have taken possession of it and settled in it, and you say, "Let us set a king over us like all the nations around us," 15 be sure to appoint over you the king the LORD your God chooses. He must be from among your own brothers. Do not place a foreigner over you, one who is not a brother Israelite. 16 The king, moreover, must not acquire great numbers of horses for himself or make the people return to Egypt to get more of them, for the LORD has told you, "You are not to go back that way again." 17 He must not take many wives, or his heart will be led astray. He must not accumulate large amounts of silver and gold.
Speaking of a man's heart being led astray, take the example of King Solomon, who had 700 wives and 300 concubines, and who ended up allowing these wives to build idolatrous temples in Israel. That was very bad!
Note that the following Biblical figures were all monogamous:
Adam and Eve
Noah
Job
Isaac
Moses
And like I posted on Ask JTF last week, all this polygamy created family problems. Take the example of Isaac/Ishmael. As a result of Abraham's mating with Hagar, we have the hateful fanatic Muslims.
There's also (for me) the very sad example of Leah, Jacob's wife. She was unloved, and resented, and she knew it! Her children, also knew on some level that their mother was not loved. Take the example of Reuben bringing mandrakes (a known aphrodisiac) for his mother.
Genesis 30:14-15 14 One day during the wheat harvest, Reuben found some mandrakes growing in a field and brought the roots to his mother, Leah. Rachel begged Leah to give some of them to her.
15 But Leah angrily replied, "Wasn't it enough that you stole my husband? Now will you steal my son's mandrake roots, too?" Rachel said, "I will let him sleep with you tonight in exchange for the mandrake roots."
This same Reuben is the one who went and had sex with his father's concubine (Genesis 35:22, 49:4). Now I'm sorry, but Reuben had some major issues. I should think much of them had to do with knowing his father did not love his mother.
And how about Reuben and all his brothers selling Joseph into slavery? That's certainly not the behavior of a happy family.
And speaking of issues, look at King David's children. Is having sex with all your father's concubines in an open tent on the roof of the house normal behavior? Or how about trying to rape your half sister?
So I guess what I'm getting at is that with polygamy, there are always the favored wives with their kids" and the less favored wives with their kids, who all know they're less favored, but were stuck in that situation, hence all the fighting and resentment.