It's an interesting contention, though I'm not quite convinced by it.
Putting Browning's argument aside, though, I think there's a pretty obvious problem with a Social Security system that simply collects taxes and disburses benefits without affording Americans the opportunity to make their own financial decisions.
Today, financial literacy in the United States is pretty dismal. I can't help but feel that most Americans would be a bit more savvy if they actually had more personal control over their money . . . and if their retirement really depended on them making good decisions.
(Interestingly, a strong plurality of Baby Boomers may be collecting Social Security income at age 62, rather than the "normal retirement age," due in part to financial necessity.)
Update: Freakonomics's Stephen Dubner points to this study on financial literacy:
[F]ewer than one-third of young adults possess basic knowledge of interest rates, inflation, and risk diversification. Financial literacy is strongly related to sociodemographic characteristics and family financial sophistication. Specifically, a college-educated male whose parents had stocks and retirement savings is about 50 percentage points more likely to know about risk diversification than a female with less than a high school education whose parents were not wealthy.