At the moment, focusing on dwindling birth rates is nonsensical because the world population is projected to be 10B people by 2050. So the issue isn't lack of people, it's the inability of various nations to properly coordinate a response to an existential crisis (global warming and increasing volume of CO2 in the atmosphere: https://climate.nasa.gov/climate_resources/24/graphic-the-re...). Dwindling birth rates in Britain should be the last thing anyone is worried about if their real concern is not having enough people in the future. I mean if they're really concerned about lack of Brits then I guess it makes sense, but globally, on a planetary scale, worrying about local birth rates is not really something to be concerned about.