God’s original intention for humankind was a monogamous relationship of equals between one man and one woman, as depicted in the Old Testament creation stories (Gen. 1:27, for example, in which Adam and Eve are both ‘made in God’s image’ clearly implying that God regarded exploitation of one by the other as part of the fallen world and not integral to the order of creation).
As time progressed, the marriage of more than one woman to a single man (e.g. polygamy) arose.
Um, that isn't supported by scripture. First of all, with the fall happening right at the start, we really have nothing to compare on the "pre fall side". It seems quite possible that polygamy was fine then too - we can't know if it was OK for Adam to take more wives because there literally were no other women on earth in the story. If there were, there is nothing in the story to say that he couldn't also have them as wives too.
As it is, it seems kinda silly to say "as time progressed", since polygamy appears about as early as there are multiple women - in the same chapter that Adam and Eve have their first child, right after the fall.
But there never existed an express biblical permission for such a deviation from the ordinance of God made at the institution of marriage in the Garden of Eden (Gen 2:21–24).
Both parts of your statement are false. First, God never "made an ordinance". The text there only says that they "are one flesh", which could apply in either case.
Secondly, God
did "give express biblical permission" for polygamy. This comes in 1Kings 15:5, where it says that "
David did what was right in the sight of the Lord, and did not turn aside from anything that he commanded him all the days of his life, except in the matter of Uriah the Hittite." David, as you probably know, had over a dozen wives. Not only does this shown that the scripture says that polygamy is completely acceptable to God, but it's also striking that a monogamous marriage is never given as explicit approval as polygamy is here.
The law of Moses censured those who violate God’s prescription of monogamous marriage
Where?
Christianity which forbids polygamists from becoming church elders.
Sure. Church elders are not to take multiple wives, just as they are not to be exceedingly rich, or so on. That was a perfect place to say that "church elders, just like anyone else, are not to have mulitple wives." But it doesn't say that. The very fact that it makes an exception to mention this for church elders shows that it is fine for everyone else in scripture.
....the bottom line is that monogamy was the old testament and is the new testament ideal; however, ancient polygamy (marriage between one man and more than one woman) was regulated rather than condemned.
This doesn't appear to be the case. Polygamy appears to be just as much a scriptural ideal as monogamy, perhaps more so, as it is the only system given God's explicit approval.
While I don't personally approve of polygamy, I have to be honest about what the scriptures say.
In Christ-
Papias