Bitcoin would be a calamity, not an economy. Fiat currency provides some forms of control, wherras Bitcoin does not.
An economy in which Bitcoin was the dominant currency would be a more volatile and harsher economy, in which the government would have limited tools to fight recessions and where financial panics, once started, would be hard to stop.
From the New York Times: As Bitcoin Bubble Loses Air, Frauds and Flaws Rise to Surface.
Bitcoin is just another bubble. (The Atlantic)