While it may be true that women were created for the benefit of men (Gen 2:18, 1 Cor 11:9), it is not true that men may do whatever they please with their wives. Paul reminded us that without women, none of us would even exist (1 Cor 11:11-12). He also wrote that men are to love their wives as Christ loved the Church. That means that we men should be willing to give up everything, even to our own lives, for the sake of our wives (Eph 5:25). We are to follow the example of Christ's daily life also, and it is clear that he treated women with the same respect with which he treated men.
We shouldn't go to the opposite extreme, either, acting as if men and women are exactly equal in all things. The Hebrew behind the term, help-meet, is ezer kenegdo, which literally means "a suitable helper or support." That term doesn't necessarily presuppose anything of authority or rank between Adam and Eve. Moses refers to God with the same word for helper, ezer (Exo 18:4, Deu 33:7, Deu 33:29). However, there is a fundamental difference between God and Eve. God chooses to be a helper at times to mankind, while Eve was created specifically to support Adam. As Paul pointed out, Eve's subordination to Adam did not begin at the Fall, but was inherent in her creation (1 Cor 11:9, 1 Tim 2:13) and evidenced by her character and mission prior to the Fall (1 Tim 2:14-15). There are other aspects of the Creation that demonstrate Adams original authority over Eve, such as the source of Eve's substance, her presentation to Adam, and her naming by Adam. Men and women are not equal in all ways. Husbands have authority over their wives in the same way that Christ has authority over the Church. While Christ willingly made himself a servant and sacrificed his own life for the Church's, there is absolutely no question that he maintains absolute authority. He doesn't force us into his will, but he makes it clear that we are expected to obey him anyway. "If you love me, keep my commandments," he said. Husbands, love your wives as Christ loved the Church. Wives, obey your husbands as the Church obeys Christ.
Polygamy is obviously not a sin. There is no commandment against it in Scripture. God's best men were often polygamists and they were never reprimanded for it. In fact, God allegorically calls himself a polygamist (Jer 3:6-10, Jer 31:31-32), and claims to have rewarded David with multiple wives (2 Sam 12:8). If polygamy always caused more harm than good, then it would be a clear violation of the command to love your neighbor as yourself. Surely God would have said something about it if that were true. He isn't afraid of men that he needs to be polite and tolerant of their sins. The Israelites who came out of Egypt were polygamous (Num 3:39,43,46) and idolatrous (Exo 32:1-26). Yet God chose to kill thousands of them for their idolatry (Exo 32:28), while giving advice on how to conduct their polygamy (Deu 21:15-17). If polygamy is not always a bad thing, then it follows that it must sometimes be a good thing.
In our fallen world, there is sickness, death, war, rebellion, hatred, and foolishness.
Yeshua and Paul said that all women should normally marry, but that there are some men who will not, and some men that should not (Mat 19:12, 1 Cor 7:25-28, 1 Tim 2:15, 1 Tim 5:9-16). The birth rates of men and women are essentially equal, and in a perfect world there would be no war and no terribly dangerous work, with the result that there would be only slightly more marriable women than men. There would be no unbelievers, and therefore no need to worry about being unequally yoked. In a perfect world, a few men would have to be polygamous in order to provide husbands for all women. But in a fallen world, war, crime, and hard labor mean that men die young much more often than do women. Making matters worse, more men than women are unbelievers. That means that in order to marry a godly man, sometimes a woman must settle for someone less desirable, steal a man from another woman, or become a spinster. None of those options is compatible with God's Law. Men don't have to be or do anything special to attract a wife, because women come cheaply. Women have to resort to marketing themselves in order to attract any attention, and we all know that sex sells. Those women who, through no fault of their own, hold no special attraction for men, have no real hope of a happy and fulfilling life, because there is no reason for any man to pay attention to them.
Polygamy can address many of those problems. A woman wouldn't have to expose herself and act like a whore in order to steal a man from another woman, because the man can be shared. The value of women would increase because there would be fewer of them on the market. Men would then be placed in the position of competing for women instead of the other way around. They would be forced to become better men in order to attract a wife. Plain, infertile, and sickly women would still be able to marry because they don't have to try to be everything that a man needs. Polygamy among godly men can benefit both men and women.
I believe that there are at least two Scriptures which require polygamy among God's people and at least one which calls it a sign of repentance. The law of the levirate at times requires a man to accept a second wife, because it makes no exception for a man who is already married (Deu 25:5-10). Paul commanded younger widows to remarry, and commanded their fellow believers to accommodate them (specifically through financial support, but by implication through finding them a believing husband) (1 Tim 5:9-16), yet he also commanded them to not be unequally yoked with unbelievers (1 Cor 7:39, 2 Cor 6:14). The only way to obey both commands is for some men to marry more than one wife. Isaiah prophesied that in the last days, God's people will be overcome by war, foolishness, and feminism. The first sign of repentance will be when women humble themselves by submitting themselves to godly men who are already married. (Isa 4:1)
Polygamy (by which I mean polygyny and not polyandry or polyamory) is sometimes a very good idea, and sometimes it is necessary for obedience to God.
"If you love me, keep my commandments," Yeshua said.
Addendum: How many verifiably monogamous men are there in the Bible? (By monogamous, I mean according to their status, not their doctrine.) In the strictest sense, we can't verify that anyone in the Bible was monogamous, so lowering the bar to "probably monogamous", off the top of my head I can only think of six, although I’m sure there must be others:
- Adam
- Noah
- Shem
- Japheth
- Ham
- Zechariah (in the NT)