And I would also like to hear some views on why polygamy could even be construed as "immoral" or "unchristian." Solomon, the wisest of men that he was, had some hundreds of wives, correct?
Solomon's many wives lead him astray from Yahweh, and Yahweh was not pleased. ( 1 Kings 11:4)
And Paul was broadly against marriage, "It is good for a man not to marry" 1 Corinthians 7:1
Indeed, Paul seemed to suggest that it was best to avoid sex, but if it couldn't be avoided, marriage was the solution. Having multiple wives would tend to undermine this teaching.
As for the broader issue: There's no compelling argument why multiple partner marriages should not be possible - but I would have thought that technically each member should be married to one another, which would mean we'd have to allow gay marriages which is scary and bad and our children will die. OR something.