Krugman explains the intellectual bankruptcy of the economics behind the most often heard case for privatization of social security. In Many Unhappy Returns Krugman shows that the economic assumptions required to generate the returns on stocks needed to earn the high returns predicted for private, personal, or whateveryoucallthem accounts require unrealistic assumptions.
And, alternately, if you believe our economy will have the kind of growth needed to earn the predicted returns, then there's no Social Security crisis anyway, because that amazing economic growth fill fund any possible future long-run shortfall.