There's complete cognitive dissonance and confusion at the moment over popular notions of national prosperity. On one hand people readily agree that the GDP is an inaccurate measure of prosperity, that wealth gained mostly goes to the top and it ought not be a prime focus, while at the same time suggest that high rates of immigration are crucial to prop up said GDP. Many countries with stagnant birthrates are rather enviable places to live, i.e. Iceland, Japan, SK. Besides a large aging population to support for a generation in some cases, I don't see the problem.