Zac Taylor at Debunking Christianity writes:
"While I think the Bible does seem to condemn homosexuality, I do not think it specifically condemns polygamy. So, Christians are in a bind here - they seem so confident to defend the 'biblical framework of the Christian family,' as the Pro-Family Network states, but what is that according to the Bible? I don't think it's as clear cut as Christians and Christian politicians would have us believe."
Christians differ on the extent to which scripture discourages polygamy. Some would argue, for example, that it was allowed in the Old Testament era, but not since then. Others would argue that it's still allowed, but isn't the best option. And some would argue, and I'm one of them, that polygamy has always been unacceptable.
There are a lot of disagreements among Christians on a lot of issues. The same is true of atheists, agnostics, Muslims, Buddhists, etc.
I'll explain why I think that polygamy has always been unacceptable. But I'll begin with the early post-Biblical sources and work my way backward.
I don't know of a single church father who advocated the acceptability of polygamy. I know of many who condemn it. Most relevantly, I can think of six different fathers from the second century alone who condemn it (Justin Martyr, Theophilus of Antioch, Athenagoras, Irenaeus, Clement of Alexandria, Tertullian). These men lived in a large variety of locations, and they represent a large variety of mindsets, personal circumstances, and theologies. They not only condemn polygamy, but even do so with much force, in multiple contexts, and with the names of specific individuals or groups they're responding to. I want to quote Justin Martyr:
"If, then, the teaching of the prophets and of Himself moves you, it is better for you [followers of Judaism] to follow God than your imprudent and blind masters, who even till this time permit each man to have four or five wives; and if any one see a beautiful woman and desire to have her, they quote the doings of Jacob called Israel, and of the other patriarchs, and maintain that it is not wrong to do such things; for they are miserably ignorant in this matter." (Dialogue With Trypho, 134)
When Justin uses phrases like "blind" and "miserably ignorant", it seems that he not only considered polygamy wrong, but also considered it to be obviously so and to a significant degree. Later in the same work, Justin comments that the followers of Judaism advocate and engage in polygamy "over all the earth, wherever they sojourn" (141). Notice not only that polygamy is an issue that Justin has to interact with as a Christian, but also that he expects other Christians to sometimes come into contact with it in other parts of the world. And although Justin obviously isn't claiming that every adherent of Judaism is a polygamist, and we know that some Jewish teachers condemned polygamy (and the large majority didn't practice it), Justin's comments do suggest that polygamy was an ongoing issue for the highly Jewish religion of Christianity. Thus, when the New Testament presents us with a monogamous view of marriage, it's doing so in a context in which polygamy was a factor. It's not as if the New Testament is monogamous only because polygamy wasn't on people's minds.
Justin attributes his comments (in a debate with the Jew Trypho) to the 130s, just a few decades after the close of the apostolic age. Later in the second century, Irenaeus condemns some heretics for trying to "introduce" polygamy into the church (Against Heresies, 1:28:2). In the mind of Irenaeus, then, there was no polygamy in the church of the apostles, and heretics are to be criticized for trying to introduce it. Tertullian attributes the condemnation of polygamy to the apostles (To His Wife, 1:2). Eusebius mentions Christians who avoid polygamy even when living in polygamous regions ("neither in Parthia do the Christians, Parthians though they are, practise polygamy", Preparation For The Gospel, 6:10). Eusebius is quoting a man named Bardesanes, who lived in the second and third centuries. It ought to be noted that the early Christians avoided polygamy even when they lived in parts of the world where it was considered acceptable.
I could multiply such comments from the patristic era. The church fathers gave a variety of explanations for the polygamy that existed during the Old Testament era, but it seems that they universally condemned its practice during this New Testament era.
Polygamy was rare in the early centuries of church history, but it did exist:
"Some peoples on the periphery of the empire reportedly practiced polygamy, including Thracians, Numidians and Moors (Sallust Iug. 80.6; Sextus Empiricus Pyr. 3.213; cf. Diodorus Siculus Bib. Hist. 1.80.3 on Egypt)...a few Greek philosophers supported group marriage (Diogenes Laertius Vit. 6.2.72; 7.1.131; 8.1.33)...Although the practice was not common, early Palestinian Judaism allowed polygamy (m. Sanh. 2:4), and it was practiced at least by some wealthy kings (Josephus J.W. 1.28.4 &562)." (Craig Keener, in Craig Evans and Stanley Porter, editors, Dictionary Of New Testament Background [Downers Grove, Illinois: InterVarsity Press, 2000], p. 683)
That last sentence is significant in that it illustrates an important distinction we should make. The issue here isn't just how widely polygamy was practiced. The issue is also how widely it was plausible, how widely it was considered acceptable or advocated in theory. As the church fathers illustrate, the fact that most of the New Testament world practiced monogamous marriage doesn't change the fact that polygamy was still an aspect of that world and one that was often encountered, particularly in theory, though not as much in practice. And part of that theoretical realm is the Old Testament. To say that the Corinthian Christians, for example, would only have rarely encountered the practice of polygamy doesn't change the fact that they would have encountered the concept of polygamy frequently when reading the Old Testament, when interacting with some Jewish sources, etc. Even if practicing polygamy wasn't a plausible option for many of the Christians the New Testament authors were addressing, it would have been a plausible option for some, and the theoretical possibility would surely be something any author would take into account when discussing the nature of marriage. Thus, when a passage like 1 Corinthians 7 speaks in monogamous terms, we shouldn't assume that the monogamous framework is merely the result of a social context.
And polygamy in New Testament and early patristic times wasn't limited to the rich:
"It had generally been assumed that only the very rich practiced polygamy, but one set of family documents that has survived from the second century C.E. shows a middle-class example of polygamy. The rabbinic writings assume that polygamy occurs and contain much legislation concerning it, but many people were unhappy with the practice." (David Instone-Brewer, Divorce And Remarriage In The Bible [Grand Rapids, Michigan: Eerdmans, 2002], pp. 60-61)
Some examples of polygamy during the time of Jesus and the apostles, examples the early Christians would have been familiar with, were Herod Archelaus, Herod Antipas, and Caiaphas. Though some Jews opposed polygamy, Josephus, a contemporary of the apostles, wrote that "it is the ancient practice among us to have many wives at the same time" (Antiquities Of The Jews, 17:1:2).
What this patristic and other extra-Biblical evidence suggests is that the monogamist tendencies of the New Testament, which some people attribute to societal context rather than the unacceptability of polygamy, are more naturally read as mandating monogamy. The New Testament authors describe marriage as monogamous because it's monogamous by its nature, not because it's monogamous only in the societal context they're addressing.
Jesus seems to have been siding with the anti-polygamists of His day in Matthew 19. David Instone-Brewer writes:
"A move towards monogamy started very early, as evidenced by a gloss in the Septuagint and other early versions at Genesis 2:24, which read 'and they two shall become one flesh.' The word 'two' is not present in the Masoretic text, but it is found very widely in ancient versions. This gloss was included in the text when Jesus and Paul cited it. Although this gloss was widespread, it did not cause the Hebrew text to be changed. Even at Qumran, when they were amassing arguments against polygamy (see below), the text was not quoted in this form, and there is no example of the Hebrew text being quoted with the word 'two' in it. It appears that this gloss was a very common addition to the text, and that it was recognized as a comment on the text rather than a variant of it. This means that the purpose of the addition must have been obvious to the reader. The gloss affirmed that a marriage is made between only two individuals, and thus polygamy is an abberation....The significant point, as far as the Gospel text [Matthew 19] is concerned, is that this variant text is used very self-consciously, with the additional comment [Matthew 19:5] 'So they are no longer two but one' emphasizing the presence of the word 'two.'...Both [the gospel of] Mark and the Damascus Document [a document critical of polygamy] cite exactly the same portion of Genesis 1:27, and they both precede the quotation with a very similar phrase. Mark refers to 'the beginning of creation'...while the Damascus Document used the phrase 'the foundation of creation'...they are semantically identical....Jesus was making the point very strongly. He was saying not only that polygamy was immoral but that it was illegal. He gave scriptural proofs that polygamy was against God's will. This meant that the man's second marriage was invalid, and thus he was cohabiting with an unmarried woman." (Divorce And Remarriage In The Bible [Grand Rapids, Michigan: Eerdmans, 2002], pp. 61, 137-138, 151)
I see at least a few indications here that Jesus was siding with the anti-polygamists of His day:
1. He cites Genesis 1:27 with Genesis 2:24 (Matthew 19:4-5), a common anti-polygamist combination of scripture.
2. He quotes the anti-polygamist paraphrase of Genesis 2:24 (Matthew 19:5), not the original Hebrew, which has a history of use by anti-polygamists.
3. He emphasizes the word "two" by mentioning it again in Matthew 19:6.
4. He uses the phrase "from the beginning" (Matthew 19:8), which is known to have been used in anti-polygamist argumentation.
It should be noted that Paul also repeatedly uses the anti-polygamist rendering of Genesis 2:24 (1 Corinthians 6:16, Ephesians 5:31). Ephesians 5 is inherently anti-polygamist. Paul tells us that there's only one Christ and only one church (Ephesians 4:4-5), then he makes that relationship the model for the marriage relationship. He also uses the head/body imagery (Ephesians 5:23), and there can be only one head and one body. Paul goes on to cite Genesis 2:24 (Ephesians 5:31). I think that the most natural way to read Ephesians 5 is as a New Testament expansion of Genesis 2. In other words, Ephesians 5 is about the nature of all marriage, not just some marriages (monogamous marriages). To argue that Ephesians 5 doesn't apply to polygamists would be like arguing that Genesis 2 doesn't either. If polygamists aren't going to get their model for marriage from Genesis 2 or Ephesians 5, then where are they going to get it?
Romans 7:3 seems to be contrary to polygamy as well. Douglas Moo writes:
"he [Paul] certainly uses the word ['law'] in 6:14, 15 and in most of chap. 7 with reference to the Mosaic law...It is almost certain, then, that Paul here refers to the Mosaic law...Since Paul does not mention divorce, we can assume that the remarriage of the woman has taken place without a divorce of any kind; and any such remarriage is, of course, adulterous. Further, any body of law that Paul may be citing - Roman or OT (cf. Deut. 25:1-4) - allows for remarriage on grounds other than the death of the spouse." (The Epistle To The Romans [Grand Rapids, Michigan: Eerdmans, 1996], pp. 411-412, n. 24 on p. 413)
Some of the most explicit passages that can be cited against polygamy are from the Old Testament, such as Genesis 2 and Proverbs 5. In Proverbs 5, we aren't told to be satisfied with our wife if she's all God allows us to have. It isn't suggested that we could seek other women if we want to. Rather, we're told to be satisfied with her throughout our life. Solomon's answer to sexual temptation is monogamy with the wife of your youth, not polygamy. Bruce Waltke cites Proverbs 5 as an illustration of 1 Corinthians 7:4-5 and writes that "Marriage is here thought of as strongly monogamous." (The Book Of Proverbs: Chapters 1-15 [Grand Rapids, Michigan: Eerdmans, 2004], pp. 317, 321) Proverbs 5:17 refers to your wife being yours alone, which can only be monogamy, and the wife is referred to as satisfying the husband's sexual thirst, which is, again, monogamy. The woman is to meet the man's sexual desires "at all times" and "always" (Proverbs 5:19), which, again, can only be monogamy. Solomon is referring to sexual relations, so he can't be saying that a husband is to be always satisfied with his first wife, even as he's having sex with his second, third, and fourth wives. Similarly, Solomon writes in Ecclesiastes 9:9 about how one wife is the reward a man is given, as if he should be satisfied with her alone.
I think there are plausible alternative interpretations to the Old Testament passages people often cite in support of polygamy. See, for example, Walter Kaiser's comments in Toward Old Testament Ethics (Grand Rapids, Michigan: Zondervan, 1991). However, even if we were to conclude that polygamy was allowed in Old Testament times, the evidence against it in the New Testament era doesn't allow us to consider polygamy acceptable today.