This article is excellent.

The difference is that established fiat currencies—ones where the bills and coins, or their digital versions, get their value by dint of regulation or law—are underwritten by the state which is, in principle at least, answerable to its citizens. BitCoin, on the other hand, is a community currency. It requires self-policing on the part of its users. To some, this is a feature, not a bug. But, in the grand scheme of things, the necessary open-source engagement remains a niche pursuit. Most people would rather devolve this sort of responsibility to the authorities. Until this mindset changes, BitCoin will be no rival to real-world dosh.