Technically, Social Security is not a Ponzi scheme.
But you can run it a lot cheaper when you have lots of young people coming into the system. The slow-down of American reproductive rates, combined with increasing longevity, do make the current system unsustainable.
I think of it as welfare for the old,
even though that's not how it was sold.
And, as a pure side-rant, contrary to assertions I hear, the boomers are not YET the problem. The first wave of boomer births was in 1946. Those people are first turning 65 this year. For the most part, boomers are still paying in!
The boomer burst is yet to come.
The outlook is worse than glum.