that's simple to solve in a functioning society just add a limit for how many children this works e.g. 3 only considering the failing birthrates of the west, maybe there shouldn't be a limit but of course immigrants will abuse it to the max once they gain citizenship, so unless they get kicked out swedes will be forced not to only pay for immigrants with their taxes but a cut on their salaries as well, to support the immigrants getting paid to outbreed them
Greece