I mean, you can't just go open your own currency exchange or forex trading business without some sort of various oversight, licensing, etc? There are all sorts of government regulations and agencies above forex sites like Oanda, for instance. And if bitcoin really is a currency, then how is setting up an exchange any different?
I can just go out an open a store that buys and sells baseball cards without some sort of various oversight and licensing.
Are bitcoins different from baseball cards?
The are not prepaid access ("stored value"), according to FinCEN.
If you are providing exchange to and from fiat, FinCEN recently released guidance on that.
If you are holding other peoples dollars, there are already regulations that address that as well.
If you are seriously thinking of opening an exchange, there are others that have done it that might be able to provide some advice. At a minimum, you'll need some capital to cover the legal fees in getting started.