I know it's a diversion but population decline is a major issue for some countries Italy for example, the problem is an economic one, people pay taxes and they consume goods and services keeping the economic circus going less people less taxes less consumption
The population problem is offset slightly by third world birth-rates which are much higher, however they have not got the economic infrastructure to cope which leads to high unemployment and grinding poverty, which leads to many trying to escape to where there is jobs and better standard of living (i.e Europe and America) this is not a new phenomenon, the huge Italian, Irish and Spanish emigration in the last two centuries was driven by much lower infant mortality, so large numbers of children were surviving into adulthood there was nothing for them so they had to emigrate
If we want to stop immigration we have to look at the reasons for it, otherwise we are just treating the symptoms rather than th eissues that cause it (less war might also help) but then again who would do the jobs we don't want to do anymore?