FinCEN is classifying bitcoin as currency and in their guidance it states:

"An exchanger is a person engaged as a business in the exchange of virtual currency for real currency, funds, or other virtual currency." 

"An administrator or exchanger that (1) accepts and transmits a convertible virtual currency or (2) buys or sells convertible virtual currency for any reason is a money transmitter under FinCEN's regulations, unless a limitation to or exemption from the definition applies to the person."

"The term "money transmission services" means "the acceptance of currency, funds, or other value that substitutes for currency from one person and the transmission of currency, funds, or other value that substitutes for currency to another location or person by any means.""

So as discussed previously in the post, it appears that: "If it is done infrequently and not for profit then that exemption applies otherwise registration is required for ALL exchangers."

What still doesn't make sense to me, is you can create an account with Etrade (https://us.etrade.com/investing-trading/forex?ploc=it-nav) and start FOREX trading; which is trading currency. To my knowledge it appears you can do that all day long for the sole purpose of making a profit. However it appears from the recent guidance, if you were to trade bitcoin for the sole purpose of making a profit, then you would need to register with FinCEN. I don't understand why someone would be able to be a "day trader" on Etrade and trade real currency for a profit, however if they were to become a "day trader" with bitcoin, then they would need to register with FinCEN.

What is the difference between trading fiat and trading bitcoin, that would require you to register with FinCEN if you decided to trade bitcoin for a profit? It appears they are both considered currency with FinCEN. I might be totally missing something, but this is what I really don't understand.