Migration is the alternative to local fertility; the working class having chosen to concentrate their wealth on fewer people. By importing labour the state doesn't have to bother with schools, childrens' health clinics. Young people from overseas are a crop to be harvested.

It is somewhat shallow analysis imo although I agree with the wider conclusion. Meanwhile, the implication you suggest is that somehow this is a static equation. In other words, there may be advantages to getting this new crop of cheap labour because of the fertility gap, but there are disadvantages i.e. provision of the healthcare/schooling etc of migrants progeny, waiting in the wings, so to speak. This needs to be taken care of. Not that they ever thought 'they' have the responsibility hehe, gap or no gap.