Sorry, I am a biology student so I see things from a biological prospective. This is what I learned in university and to be frank the world is going to be way too overpopulated (places like India, Philippines and other third world countries with high birth rates contribute significantly to this)
Poland is predicted to go into a steep decline that will last at least until the end of this century
in the next century(If we manage not to collapse from lack of energy sources to provide for this population), a higher population also means more strain on resources and a smaller one means that less resources will be required. A smaller population is economically sustainable, a large rapid growing population isn't, low birth rates and low death rates are a usual sign that a country is developed (and are ideal conditions). Immigration inst bad, but keep in mind that 1) I live in Canada and I can tell you, not all immigrant's will assimilate(and they shouldn't be forced too either) 2)
and it means that a lot of those higher wages are going to be spent supporting the elderly rather than being free for investment in the future
what do you have in mind then, Infinite growth? unreasonable. I think old people deserve to be taking care of considering that they built the economy and supported people like you. In the future I wouldn't worry about too little people, I'd worry about the opposite 3) Less people is easier to manage to ensure maximum productivity. 4) again Immigrants are not bad, but from a biological prospective they will significantly alter the genetic material (especially long prolonged immigration) from the native area.
I can go on but honestly..no one will read it.
Demographic winter is going to be a real problem for European countries, including Poland
Keep in mind Global warming, the world is changing and not static as you may think