I don't really think people grasp the idea of what privitizing social security will do to the program. Social security is meant to be there as a "safety net" to ensure a basic minimum for retired persons to live on. While the private market does have an overall higher rate of return, the stock market fluctuates and if you and if you retire in a down year, your social security payments could be cut in half. As many recent retirees have found out the hard way, a market downturn can have disastrous affects on the golden years. Retirees have a tough enough time getting a full paycheck, much less reducing it even further.
Not only is Bush playing with our future, according to a recent University of Chicago study, Bush's plan would provide a boon to the investment banks totaling $940 billion dollars over the next 7 decades. That is close to a trillion dollars going to his buddies on Wall Street. It should be no big surprise that Wall Street is one of Bush's biggest financial backers ($20.7 million to the Republicans this year alone - as reported by the Washington Post).
In addition to the windfall for the investment banks, Bush would still need to come up with the money to make up for the loss of contributions that pay for current retirees benefits. Without the contributions of today's workers, Social Security will run a $3.7 trillion dollar deficit over the next two generations. Either Bush will have to raise taxes or cut benefits. Even the current Republican house and Senate could not justify going even further into debt (well I really wouldn't be surprised if they did, but we can pray they have some sense).