I don’t personally support polygamy, but even as a Christian, I find it hard to argue against it from a Biblical stand point. Polygamy was widely practiced in the Old Testament and God didn’t seem to mind:
Genesis 16:3: So, after Abram had lived ten years in the land of Canaan, Sarai, Abram’s wife, took Hagar the Egyptian, her slave-girl,
and gave her to her husband Abram as a wife.
Genesis 29:20-28: So Jacob served seven years for Rachel, and they seemed to him but a few days because of the love he had for her. Then Jacob said to Laban, “Give me my wife that I may go in to her, for my time is completed.” So Laban gathered together all the people of the place and made a feast. But in the evening he took his daughter Leah and brought her to Jacob, and he went in to her. (Laban gave** his female servant Zilpah to his daughter Leah to be her servant.) And in the morning, behold, it was Leah! And Jacob said to Laban, “What is this you have done to me? Did I not serve with you for Rachel? Why then have you deceived me?” Laban said, “It is not so done in our country, to give the younger before the firstborn. Complete the week of this one, and we will give you the other also in return for serving me another seven years.” Jacob did so, and completed her week. Then Laban gave him his daughter Rachel to be his wife.
Judges 8:29-32: Jerubbaal the son of Joash went and lived in his own house.
Now Gideon had seventy sons, his own offspring,for he had many wives**. And his concubine who was in Shechem also bore him a son, and he called his name Abimelech.
1 Samuel 1:1-2: There was a certain man of Ramathaim-zophim of the hill country of Ephraim whose name was Elkanah [this was Samuel’s father] the son of Jeroham, son of Elihu, son of Tohu, son of Zuph, an Ephrathite.
He had two wives. The name of the one was Hannah, and the name of the other, Peninnah.
2 Samuel 3:2-5: And sons were born to David at Hebron: his firstborn was Amnon, of Ahinoam of Jezreel; and his second, Chileab, of Abigail the widow of Nabal of Carmel; and the third, Absalom the son of Maacah the daughter of Talmai king of Geshur; and the fourth, Adonijah the son of Haggith; and the fifth, Shephatiah the son of Abital; and the sixth, Ithream, of Eglah, David’s wife. These were born to David in Hebron.
1 Kings 11:1-3: Now King Solomon loved many foreign women, along with the daughter of Pharaoh: Moabite, Ammonite, Edomite, Sidonian, and Hittite women, from the nations…
He had 700 wives, who were princesses, and 300 concubines.

as well as to the slavery reference you mentioned earlier.