Polygamy in the OT

Why did God not condemn polygamy in the OT? 

Polygamy was contrary to God’s original creation intention: (Gen 2:22-24)
Polygamy was introduced by the line of Cain: (Gen 4:23)
Polygamy is mentioned as leading men astray (1 Kings 11:3, Deut 17:17)

These sorts of passages all seem to lead to a strong implicit condemnation of polgamy.  The OT prophets are also noted by the Jewish Encyclopedia to have never been polygamists, and to have often used the practice of polygamy as an illustration of Israel's unfaithfulness to God  Yet, as Paul Copan argues, there may even be a very explicit condemnation of polygamy in the OT.  Occuring in Leviticus 18:18: “And you shall not take a woman as a rival wife to her sister, uncovering her nakedness while her sister is still alive.”  As Copan points out, the sense of “sister” here may be quite broad.  In 1 Sam 1:6, we see that Elkanah’s wives Peninnah and Hannah were called “sisters,” yet were not literally siblings.  It seems that the sense is that they’re fellow female Israelites.  If this is right, then the OT does expressly forbid the taking of a second wife.  (This is the interpretation also taken by the Qumran community in the second century B.C.)

There are however passages in the OT that seem to regulate the practice of polygamy (Exodus 21: 7-11).  Do these not show an implicit approval of the practice?  No.  The effect of such regulations isn’t so much as to approve polygamy so as to regulate an ongoing practice.  Take laws that aim to regulate abortion, either by forbidding the practice after the second trimester or enforcing stricter medical rules.  The effect of these laws isn’t so much as to approve abortion as to regulate the way it’s practiced.  A similar thing can be said in regards to the OT’s regulation of divorce. As Jesus pointed out, divorce was never God’s intention and the OT regulations were given as a way to control the sinful practice.