You cut out parts of my previous arguments that contradicted your new assertions:

1) "They wouldn’t have a vested interest if ssa was a ponzi scheme ... people support ssa and don’t want to change"
First I actually already gave you a /specific example/ where it did happen for a ponzi scheme, from real life, and people thought it "works for them". Then it's simply incorrect, ponzi scheme works out for a person as long as they get out before the organizers run out of more entrants. So the participants clearly have a vested interest in it running a little longer, at least until the latter becomes impossible.

2) On "prove a negative" => "hasn't failed like one" - you twisted my words and ignored the rest of the argument. There's a study by non other than Social Security Trustees that tells you when Social Security will stop being able to make promised payments. So yeah, it's already projected to partially fail (although normally someone is delinquent on debt whether they stop paying completely or partially). Of course secondarily it's also nonsense, by that criteria Madoff's only became a ponzi when it failed, not before. Failing now or later is immaterial

Also, you yourself offered a "one is legal, one is not" argument, but when I try to explore the implications that show the argument is at best vacuous and at most can justify anything ever done by a government ("in 1850, kidnapping and forced labor are illegal, but slavery is legal, so taking someone 'eligible' into slavery is not literally like kidnapping and forced labor") you claim I'm changing the subject.

Viewing the previous thread without assuming argument in good faith, I'd actually like to retract even what I conceded about fraud/lies.

The distinguishing feature of "ponzi scheme" is not "scheme", it's "ponzi". Hence when people shorten it they typically leave out scheme, not ponzi. The distinguishing characteristic they want to indicate, is that the new entrants are paying the returns promised to the previous entrants. In that way, social security is internally constructed exactly like a ponzi. That is what I meant originally.

Obviously, nobody would invest in such a product. So, in case of an illegal ponzi, participants are duped into joining. In case of a legalized ponzi, participants are forced to join (and/or do it by default without understanding, as one does with most govt coercion). The participant acquisition method is secondary to the internal construction. And, while that is the only argument that I see where you can claim "see, not /literally/ a ponzi scheme!", if anything use of force makes it morally worse.

For lack of better terms we can call it "ponzi racket", where racket can be fraud OR coercion; or just a "ponzi".

Everything else - vested interest vs works for them, legal vs illegal, failed already/projected to fail, etc. - is ancillary and/or vacuous and/or not different between them.

EDIT:
Oh and claiming it's moral to force people to join because it creates social safety is I think (again uncharitably) your real argument; but is a separate argument I don't want to even start. Whether it even works long term, whether forced charity is moral high-level, whether it cannot be done without force, whether it can be done with force but differently (why help old people via a ponzi? just help poor people regardless of age via normal transfers!), whether it's good for society to prefer old people to e.g. children, etc.. But you are conflating "ends justify the means" argument (that can be valid) with "means are actually not the means you say they are!" because nothing bad can apparently be said about the means as long as ends are good.