I have been reading 2010s studies on fiscal impact of immigration. So many papers include quotes like: "If we assume retarded unemployed thirdies will 'assimilate,' they might make a net-positive economic contribution by next century. Policy Recommendation: Increase gibs by 1 trillion dollars."

This is barely even hyperbole; the image contains snippets from a European Commission JRC study.

Most seem to follow this pattern:
- Real-world data proves thirdies are economically catastrophic
- Authors create fictional model based on delusional assumptions
- Model "proves" thirdies become economically beneficial at some point in the future
- Sponsored by EU & UN

Fortunately, we have more recent & reliable data, primarily that released by the Danish government and Amsterdam University (see here).