Knowledge of contemporaneous needs and desires rather than presumed future interests permits the parties to make a deal that satisfies their real-time requirements and protects them against their present fears.
For the jury to accept this, they would need to accept that her husband was present at the time and applied such pressure that she had no real choice, he said.
Moreover, Congress never could have raided a system of private accounts to bankroll spending that it knew would never be supported by taxpayers if it had to raise taxes in realtime to finance (as opposed to implicitly shoveling this burden onto future generations after present members of Congress are long retired etc.).