From a Biblical perspective polygamy is not immoral.God did not forbid it;niether did He approve it. In Biblical hermeneutics there is a principle called the law of first mention. The first time a thing or event is mentioned in the Bible,it sets the example as to how the situation is interpreted throughout the Bible. In this case,God made Adam and Eve. One wife. Adam and Eve;not Eve,Susan,Marie,Mary and Cassandra.God warned kings not to multiply wives to themselves. If one did have more than one wife;he was not to marry sisters while one was still alive. If a man loved one wife more than another and the other and the first born was the son of the unloved wife;that son was to get the biggest share of the inheritence. While polygamy is not immoral;it is unwise and is frought with problems. The Oakridge Boys summed it up well when the sang;"Trying to love two women is like a ball and chain."  Think of the problems with three or more. Also Herman's Hermits said "Two girls are too many three's a crowd and four you're dead!