Re: Take away message is ...
"Reducing human population seems to be an obvious priority, but not one to which many governments want to give serious consideration."
There's only one _reliable_ way to reduce the human population and it isn't famine, pestilence or war - all three of those may give an initial dip in numbers but it's made up (and then some) in the following 2 generations.
Making people better off (wealthier) results in them having fewer children. That falling birthrate isn't just a "first world problem". Over the last 40 years as more than 100 countries have become advanced economies they've experienced the same phenomenon. Places like Singapore have switched from pushing one-child family policies to actively encouraging people to have children because so many couples decided to have none at all. China's seeing the same thing and it's starting to take effect in India along with moderately developed African countries (despite the stuff you see on TV, the vast majority of families since the late 1980s only have 1 or 2 kids, particularly in urban areas)
If you want to see where it is likely to lead, look at Japan. They call it the "lost (two) decades" due to deflation triggered by a falling population (Tokyo is shrinking and there are tens of thousands of abandoned houses in most cities) and a marked reluctance to encourage immigration. Those healthcare robots aren't there to put people out of work, they're there because there are so many pensioners need manual handling that carers are getting seriously injured trying to keep up with the workload.
(FWIW, the best way to stop "economic migration" is to try and improve the economy and governance where the migrants come from, so they don't get encouraged to risk their lives to move to a better life. Those that carp on about "bloody immigrants" are seriously out of touch with the reality on the ground in many countries. The reality is that a large amount of work _is_ going on to do just that across the world via global trading (which has so far lifted 4 billion people out of poverty in the last 40 years) and the migrants we see are mostly from warzones, failed governments or highly protectionist economies which resist change. Africa in particular is not poor, just poorly managed in many parts)