Although it may sound cold to some, the truth is that people don't consider the global population count in regards to their concerns about growth. Population growth is usually something one considers in regards to their own country, and within that country it's not uncommon to consider one's own demographic groups primarily.
As an example, I highly doubt a Japanese person concerned about birth rates is concerned about the boom in Africa and other distant nations. Japan's population is going to decline drastically in the coming years, and they don't want lots of immigration to make up for it. It won't surprise me if they do something weird eventually, like the state paying women to have children the state itself would raise. Technology like this could open up even more strange doors.
Why do people climb mountains? Why do people swim? Why do people build things? Why do people bother getting up in the morning? What's the point in living?
I feel bad for putting it that way, especially if someone younger reads it, because this can lead to developing a cynical world view that isn't necessarily valid. I'm not trying to give you an existential crisis or something, but go down the (thought) avenue completely if you're taking a trip to that destination, don't just stop in the middle of the road. People do things because they enjoy them or simply want to; life is hopefully enjoyable for most, and then sadly but inevitably we all die one day.
As an example, I highly doubt a Japanese person concerned about birth rates is concerned about the boom in Africa and other distant nations. Japan's population is going to decline drastically in the coming years, and they don't want lots of immigration to make up for it. It won't surprise me if they do something weird eventually, like the state paying women to have children the state itself would raise. Technology like this could open up even more strange doors.