This is splitting hairs. You are forcibly invested in social security so you have to pay it even if the numbers indicate you won't be able to get anything back out from it. If the distinction between this and a Ponzi scheme is having the information it's a mighty fine distinction when you have zero ability to act on the information you have.
It’s the difference between defrauding people or not, among other things. Wow.
> when you have zero ability to act
You have hit another item (do I have the option to opt in?) on the “differences between social security and ponzi schemes” bullet list, but you are pretty aggressively missing the point, I think.
It absolutely does not. Investors in a Ponzi scheme do not have the information needed to allow them to be aware of the fraud involved. In contrast, at any given point in time you can extrapolate when the Social Security system (for example - the same principle applies to any pension that isn't literally cooking the books) will need to start drawing on the general fund, or fail, if it continues operating as it is operating today.
It is a bad mistake to just characterize every non-sustainable investment scheme as a Ponzi scheme. For starters, you'd be awfully confused about what is legal and what is illegal...