is true because the real world numbers won't happen the way you say it. To quote Wiki
"it may take several generations for a change in the total fertility rate to be reflected in birth rate, because the age distribution must reach equilibrium. For example, a population that has recently dropped below replacement-level fertility will continue to grow, because the recent high fertility produced large numbers of young couples, who would now be in their childbearing years"
So unless your population all die within 30 years (i.e. one generation), the population number will not go from 1,000,000 to 500,000 in just one generation like you claim.
Completely agree with you on the next part but it is irrelevant to my point about your incorrect statement about the effect of low TFR
And your "real world numbers" is quoted from "Wiki". Nice.
No effort to argue your case eh?
Let me show you some effort of mine...
Grandfather generation: 100,000 people (Simple round number for ease of illustration)
Father generation: 50,000 people
Son generation: 25,000
That's how each generation halves itself with a TFR of 1 where 2 adults make one baby.
Now, if you know how to work out a moving average, you will see how we have edged towards becoming an aged population as it is. So the argument about a 30 year lifespan is completely missing the point.
And while we become older and older with each generation, the foreigners who come here are mostly young. No matter how you add their ages up and work out an arithmetic mean, they are young.