"Private investment plans" had little public confidence in 1930. Too many families were wiped out by the bank crashes during the Depression, not to mention the collapse of the stock market. I would imagine insurance was not able to meet its obligations either, because private financial organizations tend to raid their lock-boxes too. The reason we have SS was precisely because unregulated, laissez faire private investment failed. And it failed due to private mismanagement.

Remember what happened when Mr Bush tried to privatize Social Security? The events of just a few years later demonstrated the lack of public confidence in that plan was perfectly justified.

I have a feeling the same thing would have happened to private savings in 2008 if it hadn't been for the government bail-out. Sure, if you had "stayed put" in the market right after the Bush Recession you would have made out like a bandit, but can you say that would have happened without massive government intervention?