If we really want to save the family we must expand its boundaries. There is strength in numbers. It keeps the family weak, contracted and unsteady because it is always vulnerable to the threat of loss. With monogamy, if Mom or Dad should love another, they could not be included in the family - they must replace the spouse. Destroy the family.
Parents can get time off.
Dependency, while destructive, is often the glue of bonding, keeping people together when conflict, friction and challenges come up. In polygamy, dependency is diffused, spread between several adults, thus lessening the burden on any one person. As families become smaller with Zero Population Growth the adult to child ratio goes up, but children lose the opportunity to have siblings. Extended families or clans would give these children brothers and sisters. I have been researching polygamous relationships for over a year now in an intentional way.