That's basically a society without mass immigration - manual labour becomes more expensive, so educated people spend their time automating tasks and inventing and operating robots.
That is one of the many reasons I oppose mass immigration; a constant influx of new people makes it far, far more difficult for a single locality to figure out how best to reduce its own demand and come to a reasonably stable local identity, with an attached reasonable level of demand for goods and services.
> Do you also oppose people having more than 2 children?
Yeah, if you want to keep the aggregate demand of your society consistent, it makes sense to have fewer than 2 children. (I don't necessarily support government prevention people having more than two children, but a really self-aware group of humans wouldn't spawn uncontrollably.)
> At what point does "immigration" become "mass immigration"
The fact that you're asking me that question implies that my definition is drastically different than your definition. So- I think we can agree that if the entire population of Omaha, Nebraska (475,000) moved over the span of one month to Tahiti (280,000), that could be called "mass immigration", with disastrous consequences for the local culture, politics, ecosystem, etc. So, if you'd call that "mass immigration", which I think you'd be foolish not to, what about that makes it "mass immigration"? Whatever your definition is, it'll be different from mine.
> Whatever your definition is, it'll be different from mine.
It's not very helpful for you to say you oppose something if you are using a different definition of that thing than everyone else.
Of course I agree with you that doubling the population density of a complex society in a month would lead to negative effects, and you can use that as the threshold for classifying a situation as "mass immigration" if you want, but there's still a tautology there, as you're effectively saying you're against "too much immigration", which is true of just about everyone's position on immigration.
(I suppose some people might think that "too much immigration" cannot occur in practice, because any country that is desirable to immigrate to would have the resources to adapt quickly enough to people arriving at the rates that current transportation systems make possible).
To give a tighter upper bound, though, rather than considering the population of Omaha, let's look at the population of the whole of the US. In 2019 (so before the pandemic) the population growth rate was 0.60% per year, whereas in the past 70 years, the highest rate was 1.76% (in 1956).[0] So empirically I think we can say that the population growth rate could be almost triple what it is today without that growth rate itself being the cause of "disastrous consequences for the local culture, politics, ecosystem, etc.".
However, it is still possible that all of those aspects are negatively affected by the current population density, and that the "ideal" growth rate is negative. What all that means for immigration policy is a further step removed from the data available, but I hope that the above is helpful for thinking about these questions.