Not advanced healthcare, education, and laborious tasks such as cleaning people, and working in hot or cold cramped spaces to provide utilities.
>we are less resource-constrained in this regard than ever in human history.
Some things are plentiful, but some things are scarcer. Part of it is people have more opportunity and knowledge to choose to more preferable things rather than less preferable things.
>That Social Security is unsustainable is not due to a lack of physical resources nor manpower, but capital. Money.
Money is a proxy for manpower. For sure there is lots more room to take wealth from workers and give it to non workers, but expect more and more political headwinds and long term consequences. We have already been doing it for many decades, mostly via reducing the purchasing power of the currency (which hits workers the most) and inflating price of assets. I would posit it is at the forefront of the zeitgeist of young people feeling despondent. As I wrote before, it is trivial to know that young people today will get less than they pay in (absent the development of a robot that can pretty much do all the dirty tasks humans would rather not do).