If a balanced budget precludes the US from any future borrowing, then there will no longer be Treasury notes, bonds, or instruments of debt for pension funds and secure investments. All safe investments funds would be forced to seek insured securities on the private market. Without the US being a insurer of last resort or a guarantor to the private insurer, then we know from past experience with companies like AIG, any funds invested in the private sector would not be safe in a significant financial meltdown.
So it looks like the Republicans are making an end run to get Social Security funds.
Just a thought.