1.To divert money to the Stock Market for the benefit of the already obscenely rich
2. To make the Social Security Trust Fund available for Federal Spending.
3. To be able to tax the private funds again when the investor retires on his private account funds (if there are any remaining after fiscal and monetary fluctuations)
The Stock Market is hardly a safe investment. It is controlled by large investment groups like insurance companies, manipulated by large corporations, and fraught with opportunities for corruption and fraud.
Tax deferred private retirement funds have been available for decades: IRA's, 401K's... Some of them have disappeared leaving the retiree with nothing but Social Security.
Bush's "plan" ignores the minimum wage working poor. Does he really expect a $6 an hour wage earner to set aside a dollar or two after taxes for a private account?
What of the Social Security funds (SSI) that now pay for the disabled?