Please read my post more carefully, I wrote (emphasis added) "Social-economic systems that cause below-replacement fertility are in this way much like parasites

Please read my post more carefully, I wrote (emphasis added) "Social-economic systems that cause below-replacement fertility are in this way much like parasites" The system is the parasite, not the immigrants themselves. They are, in fact, its victims, as they will fall under the same below-replacement-fertility trap. Again, as I wrote in my post: "giving the parasite economic system a new host to feed on" - the new host being the immigrants.