Jason over at CounterColumn has this nice deconstruction of some of the more common, and commonly wrong, arguments against any sort of privatization of Social Security:

No, surpluses in the current social security trust fund cannot be considered 'national savings.' The entire surplus goes into the general fund, where it is then spent by congress. The treasury then sells a bond to the SSA. The social security surplus, as currently practiced, does not represent national savings. Every dollar represents an increase in the national DEBT.

Unless the law is changed to allow privatization in SOME form, there is no fix. Congress HAS to spend the money, because there is simply nothing else they can do with it, other than take it out of circulation.

As they say, read the whole thing.