Counterfeits

"Now they can sell those bonds in the open market - which is what should be allowed for the Social Security Trust fund bonds"

Social Security trust fund bonds cannot be sold in the open market. They have no value in their present state.

 The open market does not want them, because their future value has already been promised to future retirees ( even though the money required for that redemption has not been taxed yet ). The purchase price has already been redistributed to current retirees.

You can't take ONE bond and promise to redeem it in full to two parties. Those bonds could only enter the open market as counterfeits.