There may well come a time Goldie, hopefully not in our lifetimes, when climate change makes large parts of currently densely populated countries uninhabitable. Then we will see waves of human migration which will dwarf what we saw from Syria/Afghanistan/Africa. Many, perhaps most will die in the process, but there will still be many millions clamouring to get into the habitable zones.
Then the question becomes ‘my quality of life versus your actual life’. Tough one.
The dilemma that Windsor poses is accurate though. Our natural rate of population growth (without immigration) will soon slip into the negative, like Japan and Italy, and like Germany soon, while there are more and more aged/retired, heavy health care users. We either need more young taxpayers from abroad (who go home when they are old with company pensions), or we work more years potentially never retiring, or we cull the old. Or we agree en masse that we will take a collective hit to our standard of living, enjoy a flat or shrinking and aging population (which does have some attractions), and tax those still in work more to pay for it all. Or we abandon elements of the welfare state that we take for granted now. Loads of issues and I have no idea which direction keeps most people relatively happy, or at least not as furious as they could be.