The sad part is that all cultures with industrial-level populations could easily sustain many generations of sub-replacement reproduction rates without any risk of disappearing, if it wasn't for outside breeding pressure. It would be a shame if we ruined our planet only due to an unconstrained outbreeding race. Should we maybe accept borders (like the ones Japan naturally enjoys) for environmental reasons, to make it easier for cultures to abstain from participating in that destructive race?
And another thing: would shrinkage really be that bad, in the long term? In any case it could never be very difficult to ramp up reproduction again when needed: all future generations, no matter how low the reproduction rate of the ones before, will be descendants of a direct line of ancestors who all did reproduce, against the odds. An environment that makes it easier to resist the reproduction drive could only make that drive stronger in the next generations, due to selection.
