Polygamy has issues with excess males that aren't able to mate due to high-status males having their "harems", leading to very violent outbursts as those disadvantaged males don't have any outlet for their energy and society basically doesn't care about them beyond slaving away. China was also pretty much decaying society, which was perfectly utilized by British during Opium Wars. The typical mindset in China was to keep their old, dysfunctional ways, and add western technological advancements without replicating the conditions which allowed these to be created first, a meta-algorithm that killed Qing dynasty and that lasts until today. These days the effects of unoccupied males can be seen in the Middle East. Is that a model for your perfect stable and just civilization?