[Social Security] would work perfectly well if the population remained stable over time, or shrank. And it would even be alright if it grew slowly and linearly.
You got it right but say it backwards. The problem is population shrinking.
The generation retiring is much larger than the ones still working when population has shrunk at some point. Baby Boom wouldn't be a problem in this respect, had it been followed by Baby Big Bang.
But long-term population shrinkage can be accommodated by raising the Social Security tax (an fund-raising option that was not available to Ponzi or Madoff). As long as the generation-to-generation increase in worker productivity is greater than the generation-to-generation increase in the tax, it won't harm the general welfare.
And if that doesn't do the trick then the US can always let in more working-age immigrants.
You got it right but say it backwards. The problem is population shrinking.
The generation retiring is much larger than the ones still working when population has shrunk at some point. Baby Boom wouldn't be a problem in this respect, had it been followed by Baby Big Bang.