I know this will be hard to swallow for a lot: No polygamy is not stable and that is why it is outlawed in a lot of countries. Consider that men physiologically have a drive to produce wealth and "grow" to attract and sustain a family. (Nations I hear want that.)

What do you think throughout history the men that could not find a match did? They joined wars, became vagabonds, thieves, joined piracy or similar and went to forcefully acquire wealth and/or women (and rape). Needless to say a peaceful nation does not want that. Men are going to fight the rejection tooth and nail (a trait evolved in a similar fashion).