Your belief that paper promises of currency were viewed BY ANYBODY as actual currency is simply wrong. The constitution intended to prohibit unbacked fiat currency, and except during temporary issuances during war that is how it was until 1933.
On a related issue, Morris, Hamilton, et al argued that we needed the Bank of the U.S. They understood the fraud of fractional reserve banking but they were the fraudsters and they couched their arguments to others in disingenuous terms, such as the lack of specie, etc.
The fact remains, however, that even they did not go so far as to promote un-backed paper currency. Their intellectual co-conspirators finally pulled that one off under FDR in April, 1933.
If you believe that unbacked paper currency (as distinct from paper promises of real money) was intended by the framers, why do you think they waited until 1933 to do issue it?