> A shrinking, aging population would fix this problem. The demand for labor will go up, the supply will go down.

What leads you to believe demand for labor will rise with a shrinking population? Furthermore, why wouldn't most companies simply continue automating? While Japan certainly isn't comparable to most western nations, it's certainly a good example of the potential downsides of a shrinking, aging population. A growing one isn't possible forever, either; it will eventually level out. We've just been innovating so quickly our population hasn't had time to reach a new equilibrium.