I hope this will be helpful.
Is polygamy a sin? The standard traditional answer is 'One man is cleaved to one women.', as in Adam and Eve. If you noticed, this does answer the question directly. Yet, this answer alludes that polygamy is sin.
If polygamy is a sin then Old Testament Law forces people to sin: It was a duty to perform polygamy under certain instances in the Bible. If a man died leaving a wife with no children, one of his brothers was duty-bound to marry the widow.
`(Deuteronomy 25:5-6; Ruth 4:10; Matthew 22:24; Mark 12:19; Luke 20:28)`
Also, David and other kings had multiple wives.
If polygamy is a sin then the early Church welcomed sin: In the early church, polygamy was not barred, but regulated.
`(1Timothy 3:12)`
Polygamy can be a sin if it becomes a stumbling block: In '(Romans 14:13-21)', Paul asks Christians to conform to society if nonconformity would cause 'your brother to fall'.
In the West, polygamy is labeled a sin. Western polygamy creates a 'stumbling block' which really is sin.
In contrast are we to require a polygamist Moslem to divorce a couple of wives before he can be converted to Christianity?
Conclusion: Polygamy, though illegal in some countries, is not sin. Yet in current times, polygamy can result in a 'stumbling block'. If we create stumbling blocks for new Christians, we have sinned indeed. In Western countries, promotion of polygamy is a stumbling block. In Arab countries demonization of polygamy is a stumbling block. We Christians have to know the Truth of both God's Word and foreign cultures to be the most effective missionaries as is possible.
http://www.ctruth.com/home/beliefs/polygamy.html