So first of all... None of this applies to modern ENM (Ethical non-monogamy.) ENM can worsen male disppsability, but that's because there's systemic male disppsability in the first place to worsen and not a problem with ENM itself and is an entirely separate discussion. In the very highest classes of developing countries where this polygamy takes place, taken in isolation, it's often women who are more disposable.

However, in society as a whole, more "traditional" polygamy by its very nature is going to leave some men who are considered less desirable and those in lower social strata as lonely and unpartnered. As a result, we don't have to wonder how male loneliness will affect society over time. We have examples of what it does, and the developed world will be heading in this direction if male loneliness isn't taken as a very serious social problem.

If we don't stop demonizing male loneliness, this is what we're going to bring on ourselves.