Another effect of "single child policy" is significant prevalence of number of men over women. And it's known for making society significantly more aggressive.
I don't know if it makes society more aggressive, but women are the limiting factor in population growth so the excess men are essentially expendable, or would be but for their parents needing support.
"And it's known"...
If you are interested I recommend "The Moral Animal" by Robert Wright, book has more details on subject.