I don't understand concerns about aging populations. It's self correcting. The old people will die off leaving a young vibrant population with plenty of resources. When the elderly become a drain you simply speed up the transition by cutting off life extending medications. In fact, first country that has the political will to start terminating the elderly will have a significant advantage over the rest of the world.
China's number one goal is stability. A big part of stability for 1.3 billion people is sustainability. This includes economic concerns, resources, and (recently) the environment.
When the older generation dies off, they will still have a huge population. The future will be dictated by the ability of countries to successfully sustain and balance a robust middle class. Booming populations aren't helpful in that endeavor.
It was a much needed policy to achieve their goal.
You guys are certainly right by at least one measure: resource access. By many estimates, China will be able to domestically produce only 25% or so of its water needs within the next couple of decades and already cannot feed itself. In this sense, the policy is good, and it has helped spearhead China's charge towards a competing middle class.
But one thing about that middle class. Although China's sheer population size will keep it competing and relevant for the rest of conceivable human history (as I suggested in my first post on the matter), both the population contraction and the gender gap will inevitably result in an extended period of stagnant growth at best, if not even depression at worst (before a recovery can occur).
Take the population contraction. Since it may contract by 400 million within the next century, that means that, while the country may be much younger in 2100, there will still be fewer of them and fewer workers. While this may or may not be a necessity, it is not necessarily a recipe for sustained growth, especially when we consider the following....
The gender gap means that many single males will be without a mate. Although it is making strides, China is not a tech powerhouse yet, and it may in fact never become a tech powerhouse that appeals to even its own skilled populace, let alone an international one. With so many skilled Chinese males left without a mate and with a market that may never be as appealing to them as the US or Europe, China risks experiencing even more brain drain than that which it currently does.
Again, this may have been the necessary move for them, and I don't think there's any doubt that China will remain globally relevant and even an economic powerhouse. I do not, however, think the decision was ideal (necessary or not), and I think it could be a factor that keeps China from ultimately becoming the superpower to which it seems intent.
