If it were God's perfect and original plan, why did he only create one woman for Adam? And why did God not remove several ribs and create more women than just Eve? And why did God start over after the flood with Noah and his sons and each having one wife? Why does Scripture say that a man should leave father and mother and cleave to his wife ...instead of "wives"? It was permitted bc man is fallen. But it isn't a Biblical mandate for men to multiply wives to themselves.
I'm not suggesting that plural marriage is preferred...just not prohibited.
Mankind has a horrible history of being able to handle relationships properly to begin with...and in recent years polygamy is almost synonymous with abuse because of the way things have changed.
There is a passage where if your brother died you had to marry his wife (regardless of already being married) to produce children in his name. It's a concept referred to as the Kinsman Redeemer...it's a central theme in the book of Ruth and one story in Genesis referencing Judah and Tamar where everyone refused to give her a baby.
It's basically that we should be focused on our individual part in providing what is needed for another. An act of "loving kindness". Not perversion or self service...but giving and kindness that is needed.