So what's the long-term plan here? A country's population is just supposed to keep growing... forever?
(Long-Term question I’ve had: how does this compare with UBI, which is kinda like a pension but for everyone?)
That's not necessary. They require that the active workers (plus capital) are productive enough to keep life standards for everybody. There is not theoretical limit for how many workers are necessary. In the extreme it could be with one or zero workers.
Cows can milk themselves these days, but the cow self-milking machines can’t make themselves yet.
More workers than pensioners is required when the system works by using current contributions to pay current pensions (which is usually how state pensions work). [Which should also provides some information about how (un)realistic UBI is]
I am in a country which has the s.k. problem since a decade and since then tried to push retirement age over and over with extremely bad results (one of the higher young unemployment rate in the whole eu area).
Add to this that already now losing your job, especially if low-skilled, in your 50ies it's basically a sentence to never find another one and live under unemployment benefit until you get your small state pension.
For my generation (Born 1985-1995) it is already planned we will have to retire minimum at 74yo in the most optimistic situation. I mean, I don't even see myself capable of doing well my work at 65, and probably no one will want to keep me after 60, doesn't matter how sharp I will be. All supposing I am not gonna get pretty sick around that age, which is highly probable.
False dichotomy.
First: Employers which don’t allow people who are better suited to a role to have better chances to be hired for those roles, don’t grow as fast as those companies which do allow better candidates to get those roles.
This is basically what causes the situation in your 3rd paragraph, and is still more appropriate than relying on eternal population growth.
Second: Unless they are literally destroying value in their work (not merely being cost-ineffective, but actively damaging), then the economy still benefits from having more people working — the more value an economy creates, the more any given currency unit can buy, the more people are available to be customers, the more business can be supported by their spending, in a virtuous cycle.
This is why everyone is encouraged to work in the first place instead of jobs being treated as luxury or status symbols available to only the elite few.
But that would not necessarily be a bad thing as that would force to indeed focus on productivity growth and growth of indicators per capita instead of overall indicators.
Many of the recent advances in human rights are from people protesting, convincing other people that their plight is real, and slowly turning the tide.
In dictatorships this doesn't happen for obvious reasons so social progress can be frozen by 1 person or maybe a 1 group for decade after decade.
Similar story from Romania, where I'm from. Not necessarily with women's rights, but with other kinds of human rights.
As long as we depend on dwindling supplies of fossil fuel to send things in space, we're certainly not going anywhere.
But if we accept that the people leaving will never see the end of the journey then the problem is one of keeping a liveable, self-contained environment in space for 100+ years, which does not require crazy physics breakthrough at all, just technological advances.
This is not going to solve Earth's problems, though.
Until we get there we import people from other countries.