I think that the original intention behind the invention of currency was a good one. But no one in the Mesopotamian civilization could've known that humans would find a way to screw and break that system beyond repair. If I remember correctly, the foundations of introducing systems to screw/break the currency system were laid (at large scale) in the Roman Empire, mostly. And it went on from there. The concept of a bank, as we know them today, were popularised by different religious orders (most famously, perhaps, the Order of the Templar Knights), with the intention to protect the money of pilgrims on their way to Jerusalem (again, a good intention, which ironically screwed the Knights later when France needed money and decided to accuse the whole order of heresy (Friday the 13th)). The Medici did the rest in the Renaissance, with their introduction of how a "modern" bank/financial institution could speculate on things and how it handled interest rates etc.
Basically, humans screwed the system over time. But that's just what humans do.