Rely more on productivity rather than population growth for economic growth

Comment on David Gruen "Asia’s economic challenges and policy choices", 12/03/2014, http://www.eastasiaforum.org/2014/03/11/asias-economic-challenges-and-policy-choices/
Gruen states that “Much of Northeast Asia is facing a period of demographic ageing. China, Japan and South Korea are already rapidly ageing societies, which in China’s case is a direct consequence of its one-child policy. This will detract from future growth, yet Northeast Asia has been unwilling or unable to adopt more open immigration policies like those that enabled Australia and the United States to partially replace ageing working age populations.”
Many Asian countries have very different conditions to Australia’s, so they are unlikely to embrace open immigration programs as Australia or some other countries do.
Further, while there is an issue in terms of inter-generational balance and/or transfer, growth relies on population growth is likely to mask the importance of productivity growth.
Even though sometimes demographic dividends may contribute to economic growth and possibly productivity growth, it is by no means a certainty that a growing world population is naturally optimal to the welfare of the people of the world as a whole.
China adopted the one child family planning policy in the belief that it was, rightly or wrongly, good for the country. Of course, its one child policy has not necessarily been the best family planning policy, even if one accepted that it is desirable to limit population growth. China now seems to be changing its one child policy, albeit very slowly.
It is important to carefully consider how population growth may or may not contribute to productivity growth and based on that to make informed discussion on the role of population growth in economic growth.