Right now, bitcoin is like a country with a minuscule GDP ( * ) and absolutely no currency controls (and no possibility of such, ever). As many small countries have learned the hard way, the worst thing for your economy's and currency's stability is US and Euro-based foreign currency traders deciding that your currency is a "hot" one to trade in.
When history looks back on why bitcoin failed, I suspect a big part of it will be the SEC's decision to allow large Wall Street firms to speculate in BTC as much as they wanted to.
Now, a robustly anonymous exchange network with value pegged to something external - say, a cryptocurrency backed by EUR, USD, or actual grams of gold - that would be something different. That would likely be made illegal, either explicitly or by having nearly every transaction run the risk of a federal money laundering charge.
( * ) The GDP of bitcoin-land would be the sum total of all goods and services bought and sold with bitcoins in the course of a year.