There's gonna be a pensions crisis even at current population growth rates-- immigration is the only thing staving it off in the US and Europe, but eventually even that won't be enough. Problem with having a 0% population growth rate, or even a low rate, in modern times with good medical care, is that the population gets older, and there are fewer young people in the workforce supporting an increasingly large elderly section of the population. Given our current economic system, that's a big problem.
We just need a good nuclear war. That'll fix everything.
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