Do we really need more people? America has almost 350 million, and is completely dwarfed by India and China. That seems like plenty of people to me.
If so, that means that you need people. People younger than you. People with some sort of societal attachment to you that results in them not just tossing your entire generation into a metaphorical woodchipper, because taking care of old people is a ton of work.
The traditional way to ensure that such a population of younger people exists has been to have children. Importing immigrants might solve the "people younger than you" side of things, but it is yet to be determined if it adequately solves the "societal attachment" side of things.
If a population is depending on continued net growth it has to very careful. If there is some constant above which it needs to maintain its growth rate growth will be an exponential process and exponential processes can blow up on you way faster than you might expect.
As an example, suppose we were depending on 1% annual population growth indefinitely and bad things would happen if we could not sustain that. Let's try to put an upper limit on how long we could theoretically sustain that.
Assumptions: we do not develop faster than light travel, do not discover any extra dimensions of spacetime that we can occupy, every human now in existence is near Earth, we don't need space for anything other than holding people, and you can't pack people tighter than 16 people per m^3 (the number of present day people you could fit in a 1m x 1m x 1m cube if we were versatile shape shifters who could take on arbitrary shapes but not change our volume).
Given those assumptions, then N years from now every human in existence must be within N lightyears of Earth. Take the volume of that sphere at year Y and divide it by the number of people that would be alive in year Y at 1% annual growth and we get how much space is in the most optimistic case available per person.
Q: How long before that space per person is less than 1/16th of a cubic meter?
A: ~12000 years.
If we can drop the growth rate to 0.5% we get about 24500 years. If we can drop it to 0.1% we get around 127000 years.
Exponentials are scary.
We're pretty good at preventing people from dying young, and we're pretty good at keeping the elderly barely alive. We're pretty bad at extending how long someone can take care of themselves. I don't think we can sustain a society where people work for 40 years and then are retired for another 40. Quality of life will need to drop substantially, or we'll need massive birth rates.
You can start to see it with that new Alzheimer's drug, Aduhelm. Was originally $56,000 a year, and is now $28,000. The average prognosis for Alzheimer's is 8 years, so we would be talking about an increase of $224,000 in cost of care for an Alzheimer's patient. That's between 4 and 5 years of labor at the average wage in the US. Add in nursing home care, and it won't be shocking if a lot of people's end of life care exceeds their total lifetime earnings.
I don't have a great solution for that. If insurers reduce coverage for end of life care, the effects are going to be mediated by personal wealth. The wealthy will be allowed to retire since they can pay for their own treatment, and the poor will only be allowed to die. You can tax the rich harder, but it's only going to delay the effects for a while.
You say that, but this a majority opinion amongst people I know both in my own age group (late twenties) and my parents age group (late fifties). My circles probably skew liberal, but even so I think that most people now have first-hand experience of elderly loved ones with dementia and the effects of that on both the person themselves and those who have to care for them. I can't see many people wanting that either for themselves of their descendants.
> I don't think we can sustain a society where people work for 40 years and then are retired for another 40. Quality of life will need to drop substantially, or we'll need massive birth rates.
And massive birth rates aren't sustainable either. That only pushes the problem back a few decades. This is why I'd ultimately prefer to my life to be cut short. The only alternative on a societal level is to work much harder while I am alive. I'd rather enjoy my time here and then go and let others have their turn.
Immigrants to the US are more financially suited than Americans to the work. Same goes for immigrants in almost any country, or women, or minorities, or anyone who is willing to take a small amount of money for a lot of work. They have various and diverse cultures, just like native-born Americans do.
We are close to making fully functional life support and robotic nurses. It's more ethical to have robots do this labour than force young people out of their happiest days.
In theory you'd have the problem of inflation if each generation put all their contributions into a dedicated fund which was later used to pay their expenses in old age, but fortunately the current contributors can pay for the current beneficiaries, which mitigates that problem.
We have two potential paths as a society between a return to Serfdom, and a future where people still own things.