Your substitution would make that sentence nonsensical. We can’t begin pure and through action be revealed to actually be impure.

Both Rousseau’s and Franklin’s views have utility. One requires one to express one’s inherent goodness. The other defines whether one is good by whether they do good acts. These both promote good acts.

Taking inherent nature from Rousseau but ascribing bad acts to that inherent nature just means no one is truly responsible for their actions. If they are good they do good. If they are bad it is because they are bad. Anyone believing they are just “a bad person” has no reason to even try to be good except to avoid consequences. It’s a bigger cop out than “society made me” while simultaneously puritanical in ignoring the role of outside influence like society.