At least in America, “less immigration” won out over “more immigration” by clear polling margins every year since 1965, except for a few years in the 2010s. Democratic processes gave them more.
I’ve seen similar results in the UK. Parties mentioning immigration restriction consistently do well and then end up doing nothing or increasing it.
Obviously colonization is only one kind of mass human migration and there are important differences between it and the migration now ongoing, but I don't think "the choice of the people already there" is really a factor in either. One could also argue that in most cases, a determined effort to repel colonizers would have prevented colonization. There was no such societal consensus, so it happened.
> Also, it would not work. Germany still attracts foreign workers in some fields (e.g. nurses). If you tell them, they get to work for 15 years and then have to return, no one would come. If the indigenous people of Germania advocating for no labor migration are ok with dying in their own excrement, because there are no nurses, I guess that would be one way to solve the problem.
Why wouldn't more young Germans just go into nursing? This seems like a rather exaggerated doomsday scenario. There would be shortages, wages would have to rise, and more Gerrmans would choose nursing over what they choose now.
Further, since birth rates are dropping everywhere, aren't you just buying yourself a few years? Eventually everywhere the immigrants are coming from will have the same problem you describe - and their home countries will be in horrific shape because you've sucked away all their talent. What happens then? This is a shortsighted policy no matter how you look at it.