Human's at scale are fungible. "Destruction of productive and healthy societies by prolific but unhealthy ones". I hesitate to use the word dog whistle, but this is pretty inarguably racist. Unless you'd like to clarify which 'unhealthy' cultures you're referring to. For many value judgements, the lack of social cohesion, level of violent crime, historically high rates of imprisonment etc make the US an 'unhealthy culture'.
- Immigration will alter the societal outcomes of a region, for “better” or “worse”, as the region chooses
- Destruction of productive and healthy societies by prolific but unhealthy ones will cause widespread harm.
- Failure to reproduce at replacement levels won’t show up as a disaster until many years after it is too late to correct it.
Wouldn’t it be better to aim to reduce harm and increase productivity, than to blanket reduce the overall population?