It is literally the case that the later taxpayers are paying for earlier taxpayers' social security.
It's not formally a Ponzi scheme, because it's not entered to involuntarily, it is forced.
Social Security is a defined-benefit entitlement, so its spending requirements are fairly predictable. The rate of growth of the economy and the population, on the other hand, is not so easily predictable. This is why the Social Security trust fund was established in the 80s -- to patch the gaps that would result from the smallish Generation X paying SS for the Baby Boomers.
Depending on how long the Baby Boomers live and how the economy performs over the next few decades, the trust fund may run out in the next few decades. This will require either a cut in benefits or additional revenue for the system. Adjusting the inputs and outputs for a program to keep it in equilibrium in a chaotic, unpredictable world isn't fraudulent or a sign of a broken program.
So no, I'm not aware that Social Security will become insolvent in the future. Any of a number of fairly simple adjustments between now and then would prevent the projected benefit cuts. Even in the absence of a fix, Social Security will still pay out the lion's share of its promised benefits.
What you call "additional revenue for the system" is actually a government bailout by tax increase (plus inflating the money supply).
It is absolutely fraudulent. It is fraudulent to force me to invest in a fund when I want to invest my money elsewhere because I think I can get a higher return.
It is also fraudulent to force me (as a taxpayer/holder of USD) to bail out such a fund.
I called it a "Ponzi scheme" because of the idea that later "investors" pay for the prior generation of "investors"---which, like a Ponzi scheme, fails (and requires a bailout) when the next generation isn't large enough.
Admittedly, my definition of "fraudulent" above isn't true in a strict accounting sense. AFAIK the books are essential "open." Nobody is being deceived. However, it is someting worse than being deceived. It is knowing the unfortunate truth, but being forced to "invest" (and to "bailout") anyway.
