IMO the answer is not ever more people- planet earth is being destroyed by too many.
If we were able to build a rocket to go to the moon using slide rules, we can find a better way, if we want to- I suspect we don't really want to deal with it- so much easier just to breed more people.
Just a thought, but if Japan doesn't want to let in more immigrants, send the old people to other countries with high unemployment to be looked after.
More people are retiring and fewer people are paying into the social safety net.
I suspect that Japan is very wealthy, but most of the wealth is in the hands of very few, as in most countries. Let's redistribute the wealth then. Problem solved.