Except the population (at least in my country) is quickly growing anyway because so many refugees come. And there will be far more if climate change continues at this speed.
Edit: this comment isn't directed against immigration (judging by the downvotes you probably interpreted it that way), I'm just stating the way it is rn
3 people in a 737 don't make 100people non matter what side they seat at or how many times they change seats....but if they seat at the right place near an emergency exit with no seatbelt on, they could make it 2 people or even 1 person in the plane!