Interesting post, though it should be noted that there is some truth in what he says. Rapidly dwindling birth rates in developed countries are starting to pose a threat mainly because of the way societies are set up. Which is as basically giant Ponzi schemes where the young pay for the old by joining the workforce which sustains society.

But like in any Ponzi scheme, when the new members are not numerous enough to sustain the old ones inevitably it collapses.

So, in developed countries there is a need to start increasing the birth rate up to around 1.8/2 per woman, which would stop the descent of lower standards and higher costs for younger generations whilst keeping the population size under control.

The problem is of course having children is becoming increasingly expensive due to our continued technological advancement, which paradoxically leads to increasing difficulty in raising children, which is leading more people to choose not to have children due to not being able to afford to.

In developing countries of course the problem is the opposite, it is to stop the explosive population growth which is pushing them further into poverty. The way that is done is simply by helping them to reach developed status.

So, there are two problems really going on, in developed societies the birth rate is dropping too low while in developing countries it remains too high. The solution for the developed society problem is to break the pattern of increasing child care costs, for developing countries it is helping them to reach developed status.

Neither of these feats will be easily achieved, but the need to achieve them will likely become increasingly important as we progress through the century.

Though it should be said that Elon Musk's blanket statement does not serve to help in the battle to achieve either of these feats, so fair play to calling him out on it.