I read the links in the first post - very interesting and it's good to see it laid out.
Supply and demand issues for resources (food, water, etc) normally sort out excessive populations in nature - too many predators for prey, the predator population crashes, etc. The same will apply for humans eventually, although the survivors will be based on who can control the resources and fend off those that want them. It will be equally messy, brutal, inhumane and downright grim when this becomes more of the norm in the world.
Population control or reduction will never be achieved through any means of self-control or enlightenment. It will only ever occur through making alternatives available that make reproduction less appealing. Western society has done that (sort of) by consumerism and increased standard of living - you need to money to buy stuff however raising a child cuts into the money you could otherwise spend on stuff - it's a tradeoff.
Our means of consuming and higher standards of living can't be replicated for everyone with our current approach - not enough energy, too much of the wrong type, limited materials, etc. However, I wonder how far we would need to uplift living standards and consumerism world-wide to get the voluntary population reduction choices we're seeing in Western society? And what parts of these would have the greatest effect? I suspect even the minimum baseline would be too hard to achieve (mostly because of politics, religion, greed, etc), but it would be interesting to know.
And of course, raising the living standards would actually make the population issue more of a problem in the short term as you're likely to increase life expectancy...