> just search for countries by gdp/debt %. It's been just incresing for decades, that is not sustanaible
This is an idealogical argument more than a factual one. It certainly appears to be sustainable.
Step back from the gdp/debt ratio figures though. The argument is really only about whether a decreasing workforce can support an increasing population of retirees.
If government pays retirees then retirees get a direct payout, and use it to buy goods and services that younger people provide.
If (like in Australia) we make everyone invest through their life then each has a well-funded retirement account largely tied up in the stock-market. This represents part ownership of assets in the productive economy, which can be converted to funds that retired people will use ... to buy goods and services that younger people provide.
Where the money comes from seems less important to me than the fact if there is an ever increasing population of retirees, then one way or another they are supported by working people.
The mechanism is just an abstraction. The demographic problem is probably more real.
