You can read the Bible as a rule book or as an insight into the ways of G-d and His relationship with His people. It has elements of both.
David's plural wives were not condemned directly, although they were condemned in the passage about not multiplying wives. But it was clearly David's willingness to ingulge his appetites, including multiple wives, that eventually lead to his most egregious sin - the murder of Uriah to cover up David's adultery.
The concept is also made clear when Abraham tries to fulfill G-d's promise through Hagar rather than his wife Sarah. G-d does not bless Ishmael nor pass the promise through him. G-d blesses Isaac who is the product of Abraham's only legitimate wife.
Abraham had no reason to think he was wrong to father a child through Hagar. It was normal in Chaldean society for men to do this to have an heir. However, G-d's ways are not man's ways. G-d went to a lot of trouble to bring Abraham out of Chaldea to a place where G-d could teach Abraham what He wanted for us. And in the issue of marriage Ishmael and Isaac became the focal points of the lesson. G-d intends for a man to marry one woman and to father all his children through her.
Keep in mind that G-d also doesn't condemn divorce. He actually creates a law for it. But He also makes it clear that He hates it. While we are fallen He makes allowances for things that He doesn't intend. Our goal as the fallen is to try to give Him what he intends - not look for excuses to do things our own way.
Shalom.
Abraham did not "try" to fulfill God's promises through Ishmael. He knew which lineage was the one of promise. That is why he took Isaac with him for the sacrifice and not the son of the bondwoman.
I'm not saying Abraham was perfect, but I don't recall any scripture ever saying he was evil or wrong for having more than one wife. To the contrary, I only recall Abraham being referred to as "righteous".
I agree there are, and have been, cultural conditions that make certain practices desirable or necessary, and God allows man to do them while it is appropriate. However, I also think those that practice polygamy today are doing so under their own desires while trying to fool us (and likely themselves) into thinking God wants them to do it. This is the essence of "...multiplying wives unto themselves...".
As a matter of faith I do not believe that was the case with the Mormons from ~1840 to 1890.
:^)
As far as Abraham you it got kind of close. Abraham's mistake was he lost faith in what God Had told him. At the bequest of Sarah he took Haggar as a concubine (wife). Haggar had Ismael. Sarah had Issacc. Because Haggar was a concubine Isacc was in line for the inheritance. It had nothing to do with adultery. Abraham later married Keturah also.
If God does not condemn divorce which he hates then how do we know he condemns polygamy which He never says he hated, but in fact said He blessed many men with multiple wives ie. King David, Samuel.
And the law for divorce was ?????????? because of Moses God allowed divorce BECAUSE OF THE HARDNESS OF YOUR HEART. So all one is saying when they get a divorce is that they are hard hearted