Polygamy, especially in countries with smaller populations, would result in massive inbreeding which is never a good thing. It would also make the dating market an even bigger disaster than it already is as there would be much less available women, unless cheating becomes normalized, or the women are polygamous too so that it goes both ways, which sounds like something that would end up in total chaos.
I think strict monogamy is the favored relationship model for good reasons, and the reason why we in the West have built the type of stable societies we have now. We may not have the biggest populations, but at least we are a population of quality people. Many countries around the world wouldn't be as poor as they are if their populations were reduced by 80% because of polygamy, rampant promiscuity, and having many children for no reason other than "family honor".
