Nobody said 'caste, second class or non-citizens' though. Yes, people who have the 'colonialist mentality' might assume that foreign-born people are only capable of replacing menial workers, but that's not implied by the basic logic that if people are born below the population replacement rate some countries and above it in others, some population transfer might be desirable and not consistent with much of the reality of immigration.
The British government has gone backwards on this: a British-born child of non-British parents was stripped of her citizenship, barred from the country, and denied legal appeal. https://www.bbc.co.uk/news/topics/c347vzp58nzt/shamima-begum...
All the rhetoric which drove repatriation of the Windrush migrants [a much more representative case than Begum leaving the UK to join ISIS] was based around the popularisation of the idea that the UK was 'full' of 'unsustainable' numbers of migrants. So it certainly doesn't help immigrants to pointedly refuse to state reasons why this is incorrect.
> the GDP [of Japan] was lower last year than it was almost twenty years ago
That is an extraordinary claim that's contradicted by brief searching: https://tradingeconomics.com/japan/gdp-constant-prices