My brilliant colleague Jagadeesh Gokhale explains why the notion that personal accounts and Social Security solvency are unrelated is a canard.
Here's the core of the argument:
The difference between the two projections of future benefit levels funded out of present law payroll taxes — higher ones under “add-on” personal accounts versus lower ones under a “status-quo” hike in payroll taxes — constitutes the basic case for “carve-out” personal accounts. How come? If “add-on” accounts to pay for benefits that are promised but unpayable under present law effectively increases saving and investment and preserves work incentives, the (lower) level of payable benefits under a “status quo” payroll tax hike could be financed with a less than 12.4 percent payroll tax rate under the “add-on” policy. That implies room for a “carve out” — that is, for diverting a part of present law payroll taxes into personal accounts.
How large would be the size of a feasible carve out? Would it ultimately completely do away with the need for “add-on” contributions? These are difficult questions to answer. Two considerations suggest, however, that the scope for carve-outs could be large. First, several studies report that payroll taxes add significantly to marginal tax rates — especially for households' secondary earners — and that labor supply is quite sensitive to higher taxes. Noteworthy here is a recent study by economics Nobel laureate Edward Prescott that attributes the significant decline in European labor supply relative to the United States since the 1970s to higher European social insurance taxes.
Second, loss in annual output because of the savings-reducing impact of the current Social Security system's pay-as-you-go financing structure is estimated to be of the same size as total current outlays on Social Security. That is, were the existing system based entirely on “add-on” personal accounts, the gain in annual output due to higher saving and capital formation would have been about as large as total current outlays on Social Security.
It's a complicated argument, but nobody ever said getting it right is easy.