If no one knows what these assets are really worth, how can you be sure that they are selling them to the treasury at a loss??
They could be selling something to Paulson at 60% of face value which might truly be worth only half that.
This provision effectively outlaws sales of the securities to anyone but the treasury, since buying them now from a bank at a distressed price, will prevent anyone doing so from having access to the treasury facility, while their competitors will have and will use that access.
Paulson's original intention was to create a market for these securities and support their prices. The congress provision is there because they feared a banker somewhere might make money, and they can't have that! So instead, they made a parking space, not a market.
The congress is financially and economically illiterate, and every single provision they added was designed to help the treasury and to screw the banks. Guess what? Screw the banks hard enough, and you won't have any banks to screw.