Indeed, it seems like the drag from having an older population does a lot to keep the birth rate down.
Our best forecasts show Japan's population pyramid as still markedly inverted and still shrinking in 2100.
(I don't agree with your other point either, necessarily, but I chose to ask about this one).
Death. And there are trivial ways to keep fertility at replacement level and not negative, on par with most other 1st-world countries.
A perpetually inverted pyramid would require that fertility rate shrink even further, until it approaches 0 - do we have a reason to believe this will happen?
Notwithstanding, in 100 years the entire global population growth is projected to stagnate, which will make this a moot point. No one will be able to rely on immigration to grow perpetually.
That is incorrect.
(I'm assuming that the life expectancy does not change significantly)
Any fertility rate that's below replacement maintains an inverted pyramid, if you don't have a lot of death before old age. (Until the very last person dies, in a long long long time).
Each person in the current breeding population produces fewer people in the next breeding population; this produces an inverted pyramid.
> And there are trivial ways to keep fertility at replacement level and not negative, on par with most other 1st-world countries.
No country that has fallen into population decline has found these "trivial ways" in modern times. (Not sure what you mean here by "negative")
It’s like mandatory military service, except for women.