You bring up the point of some of the confusion around the issue. For instance here is the bible on slavery which is hardly condemning:

1 Timothy 6
1All who are under the yoke of slavery should consider their masters worthy of full respect, so that God’s name and our teaching may not be slandered. 2Those who have believing masters are not to show less respect for them because they are brothers. Instead, they are to serve them even better, because those who benefit from their service are believers, and dear to them. These are the things you are to teach and urge on them.

From the other side, Gluttony, a Deadly Sin, has always been legal in the U.S. Take for instance the deadly and unhealthy gluttonous consumption of cigarettes, which is as you say, “NOT natural or normal. Unhealthy for body and soul.”

In Africa today men marry more than one wife as a way to achieve status, as if they too were rulers. This is why polygyny is sinful. It is motivated by a desire to achieve worldy status, something Christians are not to do.

For more on this, read these short essays:

http://jandyongenesis.blogspot.com/2007/07/chrysostoms-interpretation-of-lamechs.html

http://jandyongenesis.blogspot.com/2007/04/story-of-lamech.html

http://jandyongenesis.blogspot.com/2007/05/lamech-segment-analysis.html

There is no letter on polygamy or change of teaching from the Church of Nigeria.

This is an old story that a Nigerian newspaper picked up this past week. It was then reprinted on the various blogs and listserves and used as a polemical cudgel to make a point.

The fact that it is a false story will not be of the slightest importance to those who have taken up the cry against Archbishop Akinola.

Read the original documents at:
http://www.anglican-nig.org/Nnewi2008PASTORALletter.pdf (page 2 and also paragraph 15 of the Nnewi Communiqué http://www.anglican-nig.org/Nnewi2008Communique.pdf )

The Church of England Newspaper also had a story on this issue back when it was news.

Murder, adultery, multiple partners, slavery and theft: all are wrong and condemned in law, either biblical or civil. But guess what: they are “normal” human impulses.

Homosexual behavior: prohibited by scripture but recently decriminalized in civil law. Aberrant or deviant behavior, to wit, NOT natural or normal. Unhealthy for body and soul.

Question: Which category of behaviors should we normalize and sanctify by church blessing? Answer: neither. especially not the latter.

The last time a western culture was challenged with this issue was in England after WWI. At the time the armed forces of England were made up of units from sections of the country. As is usual in war some units have more loses than other. After WWI there were communities which were very lacking for men. While polygamy was not the answer, nor should it have been, some towns were very disrupted for a generation. Loses are part of war and after WWI units were made up of people from across the county so this social problem did not repeat.

In the Old Testament times, a look at the loses for the Jewish nation suggests that there may very well have been a lack of men in society. Holy Scripture suggests that a very great number of men under arms so at times there were great loses. In theory a society could withstand the lose of a great percentage of its men if polygamy were allowed for a generation. That, I suggest, is why it was part of Old Testament society.

Polygamy is like slavery. It is not exactly prohibited by Holy Scripture. On the other hand that does not make it proper.

In a more primitive nomadic warrior society with enemies all around, polygamy is beneficial for society in two ways:

it allows women to come under the protection of a strong warrior, and

it allows for more children to be born to replace the warriors who fall in battle or die later of their wounds.

This was the situation in ancient Judea, dark ages Mongolia, and the early Mormon church. In times of peace, polygamy tends to die out. In times of war, it becomes almost a societal imperative and informal polygamy, like the recognition of cadet and bastard branches of a noble house, fluorishes.