Those are pretty typical arguments among Christians. They are dishonest and slimy arguments. I find them infuriating.
I think teachers sometimes offer such arguments out of ignorance, really not knowing any better. In that case, maybe they shouldn't be teachers.
On the other hand, teachers sometimes make such arguments dishonestly, when they really know better but are embarrassed by the Word of God, and are afraid of the disapproval of men and women. In that case, maybe they shouldn't be teachers.
It is really discouraging to see the 119ministries guys making such arguments. They supposedly take God's law seriously.
It is dishonest to say that the Bible "discourages polygamy", and therefore nobody should practice it. People also suggest that God tolerated polygamy in the OT, but really doesn't want people to do it, especially now. Such arguments are an assault against the holiness of God.
God is Holy, Holy, Holy! He is Light and there is no darkness in Him. He doesn't wink at sin and let it slide.
God established marriage and declared it good.
Something is either sin or it isn't. Polygyny is either marriage or it is adultery/sexual immorality. The Bible very clearly treats it as marriage.
I don't know if polygamy would exist in some hypothetical world where Adam never sinned, and death never entered. Frankly, that doesn't matter. We don't live in that world. We live in this world, and God's law in this fallen world undeniably regards polygyny as marriage.
I don't know if polygyny is "ideal" or "discouraged". I don't know if any particular man should enter into multiple marriages. God Himself regards polygyny as marriage and that is that.
A few years ago, my brother in law was tragically killed in a car accident. Last year my sister remarried (normal mono). Was her remarriage "ideal"? It never would have happened if sin hadn't entered the world. In a "perfect world" my first brother in law would not have died. In a perfect world my new brother in law's ex-wife wouldn't have been an adulteress woman who abandoned her husband.
It doesn't matter. Remarriage after the death of the husband is totally lawful. It may or may not be advisable, but that isn't the point. (By the way, my new BIL is awesome, like my deceased BIL)
The point is her marriage is legitimate, just like polygynous marriage is lawful for man.
Look at Leviticus 18, where the Law discusses sexual sin.
Does God "discourage" adultery with another man's wife? I don't think so. He calls it an abomination, says not to do it, and says that practicing it merits death.
Incest, homosexuality, beastiality are all pretty much treated the same way. Don't practice these things. They are abominations in the sight of God, and merit death.
Marriage on the other hand is declared good, and blessed by God. Both monogyny and polygyny are marriage.
Our Father in Heaven, we pray that You will raise up courageous men, those who tremble before Your Word, to be teachers of the Church. We ask this in order that Your Son would be honored and Your people be built up.