Why should I pay for your locally-grown children when I have alternatives? Say each woman has maybe one child late in life, so the population has a half-life o

Why should I pay for your locally-grown children when I have alternatives? Say each woman has maybe one child late in life, so the population has a half-life of about 35 years. In exchange, I get to double the educated workforce of my society, which makes it produce more economic output. I also get the performance advantages of diversity. The only thing I have to do to keep things working is attract a number of immigrants equal to 50% of the population each generation. Which, because the scheme generates lots of wealth, is not hard to do. So what's the value-add for your alternative?