Re: Elon Musk: population collapse biggest threat to humanity
I do feel reminded of pyramid schemes reading through the arguments here, be it fertilizer or population: ever greater quantities being required to enabling ever diminishing returns.
But then the 'growth of the economy' is dependent on that, after all the markets (and with it profit) can only expand if the consumer base is expanding right? Which then leads to the thought that economy (at least stock markets) is bound to collapse unless the pyramid keeps on growing.
I reckon that collapse will come way before any population collapse (at overall stagnation already) - if you can't make profit by investing money because the market stagnates would seem a somewhat greater existential threat then a declining replacement rate.
But back to the premise of the OP - I don't think that population collapse in itself will the issue, rather it will be a trigger, on a local scale, that then dominoes. The fragility of the global supply system (and it's interdependence) has been ably demonstrated over the past few years, so I think it's not so far off that a local population collapse will have drastic, global consequences.