The problem is, the Bible rarely makes commentary on historical events. If it did, we would see notations like "[and this was not only sinful but STUPID because God's plan for marriage is one man, one woman for life, and bad things happen when we disobey His commandment]." The fact that sinful, unwise behaviors are recorded (without commentary) in the Bible doesn't mean it was OK any more than newspapers reporting on crime means they condone it. They're both just telling you what happened.
According to the Bible at 1 Corinthians 7:2 God does not approve of polygamy. The scripture clearly states 'Yet, because of prevalence of fornication, let each man have his own wife and each woman have her own husband.' According to the New World Translation of the Holy Scriptures