Most of the arguments here aren’t very clear. For example, Abraham married was polygamous and had to deal with jealous wives and one son and wife being exiled. Nonetheless, God doesn’t bother to actually come out and say “don’t do polygamy” or “all this bad crap happened because you were polygamous”.

Yes there’s plenty of examples in the Bible “polygamy is wrought with favoritism, fighting, jealousy, and mistreatment ” but is this to teach that polygamy is bad or is it to provide a history of events? The Bible has plenty of cases of Kings and Princes who are petty, corrupt, cruel, and do a lot of mistreating of others. Yet few people consider the Bible to be an indictment of monarchy as a form of gov’t. It seems just as likely that a fair reader could take the Bible as warning that polygamy carries with it the dangers of ‘favoritism, fighting, jealousy, and mistreatment” and the polygamous reader must be on guard for those risks.

The best argument I see the author presenting is Matthew but even there it’s not exactly 100% clear. Why couldn’t the man and woman ‘become one flesh’ and then the man becomes ‘one flesh’ with his other wife and so on? Clearly at this point in history the Jewish people had become monogamous because Jesus elsewhere warns that the man who divorces his wife and marries another becomes a bigamist. So obviously at that point having multiple wives was not permitted in Jewish law. But one has to wonder why couldn’t the OT or the NT for that matter simply state point blank that polygamy was over the line?