OK, maybe I am engaging in a bit of hyperbole, but the fact remains that there is no way to "opt out" of the system, so it's a forced savings plan at best.  Taking someone's money by force is called "robbery" if an individual or business does it.  Now, let's take those three attributes you cited that constitute a Ponzi scheme:

1. Ponzi schemes entail deception, whereas Social Security is exactly as advertiized-- current workers pay into the system, and that money is transferred to current retirees.

No deception?  What do you call that non-existant "Social Security Trust Fund" that lawmakers of both parties use as political fodder at election time?  There hasn't been a Social Security Trust Fund since it was combined with the General Fund in 1968 to cover the deficit.  Furthermore, when FDR first enacted the program, he promised that participation in the program would be "completely voluntary".

2. Ponzi schemes are inherently unsustainable, whereas Social Security can be-- it only requires that politicians adjust taxes and benefits to account for a shrinking workforce and an expanding population of seniors.  In fact, if demographics were constant, Social Security could continue indefinitely without any change at all to taxes or benefits at all.

Yes, but the demographics don't remain constant in the real world, do they?  I also noticed how you studiously avoided using the words "raise taxes" and "cut benefits".  That's what I love about the left.  They never stop to consider that what they've been doing is wrong; they just think they haven't spent enough of our money on it yet.

3. Ponzi schemes are designed to enrich the originator of the scheme.  Social Security was designed to "enrich" old and disabled former workers, who were often destitute before Social Security was enacted.

Well, my 76-year-old mother would probably tell you she doesn't feel very "enriched" by the pittance she gets.  Mostly the program now just "enriches" the careers of politicians who like having it as an issue to demagogue at election time.  Social Security may have been started with the best of intentions, but we all know the saying about good intentions, don't we?

Regards,
Scott Perry