yep, there are countless flaws in this. Of course, there are countless flaws with cash, too. Counterfitting, theft, quick change artists, slugs in machines, lost money, productions costs of minting the coins, security of the minting tools to prevent couterfitting, money that wears out (you know - the coins that don't work in the soda machine). And those are just a few off the top of my head.
No system is perfect. Identify the falws in whatever system you want to use and work to minimize them.