Peter W. van der Horst, "The Interpretation of the Bible by the Minor Hellenistic Jewish Authors," Mikra: Text, Translation, Reading and Interpretation of the Hebrew Bible in Ancient Judaism and Early Christianity, ed. Martin Jan Mulder (Peabody: Hendrickson, 2004) 531-532.
van der Horst discusses Demetrius the Chronographer, who lived in the third century B.C.E. Demetrius held that Moses' wife, Zipporah, was the descendant of Abraham and Keturah. Demetrius also maintains that Zipporah was the same woman as Moses' Ethiopian wife in Numbers 12:1. According to van der Horst, Demetrius was trying to show that Moses was not polygamous. This possibly indicates that polygamy was frowned upon within the Judaism (or a Judaism) of Demetrius' day.
A lot of western Christians are puzzled by the existence of polygamy in the Hebrew Bible, probably because it's a marked contrast from their own monogamous culture. Moreover, since it's done by holy men in the Bible, they wonder if God himself sanctions it.
On the "no" side, we see a lot of strife when a man takes two wives, particularly in the case of Jacob (Genesis 29). Leah and Rachel were often at each other's throats, and anti-polygamists affirm that this shows it was not God's will for a man to have more than one wife, even though God may have tolerated it (see Deuteronomy 21:15).
On the "yes" side, God says to David through Nathan in II Samuel 12:8: "I gave you your master's house, and your master's wives into your bosom, and gave you the house of Israel and of Judah; and if that had been too little, I would have added as much more" (NRSV). Here, God not only appears to tolerate polygamy: he actually blesses David with more than one wife!
Some evangelicals argue that Jesus abolishes God's tolerance for polygamy in the New Testament. Jesus says in Mark 10:11-12: "He said to them, 'Whoever divorces his wife and marries another commits adultery against her; and if she divorces her husband and marries another, she commits adultery." This is a radical passage in light of the Hebrew Bible, in which a man could have lots of women simultaneously, whereas women could only have relations with one man (at a time, that is--women were allowed to remarry as widows or divorcees). Here, Jesus affirms that a husband can actually commit adultery against his wife by leaving her for another woman. Is this the prelude to a Christian ban on polygamy and insistence on monogamy? Perhaps.
Moreover, in I Timothy 3:2, 12, "Paul" mandates that bishops and deacons be the husband of one wife. Polygamy looks less than ideal in God's eyes, as far as this passage is concerned.
As far as Judaism goes, the Encyclopedia Judaica and the Jewish Encyclopedia (see here) maintain that rabbinic Judaism frowned on polygamy yet permitted it, provided that the husband took care of all of his wives. Only in the tenth century did Judaism officially ban polygamy.
Demetrius may have disapproved of polygamy years earlier, in the third century B.C.E. Even if Judaism allowed it, it was still distasteful to a number of Jews, and Demetrius possibly wanted to show that a man as illustrious as Moses did not engage in that kind of behavior. But how did he explain away the polygamy of Abraham and Jacob, who were patriarchs? I don't know.