One makes money trading because somebody else is willing to take a bad deal. This happens because they are motivated (need to do the trade for outside reasons), don't have all the information you do, have the information but have come to bad conclusions, or are just dumb and not thinking. Bitcoins are currently used by "geeks" aka smart people. Thus, you are unlikely to find trades that are good for you. Trades you THINK are good are probably going to end up bad or breakeven for you, and the other guy simply has more information than you do.
When I first started in bitcoin, I traded bitcoins for paypal at an amazing rate and thought I'd made out like a bandit. Then I realized that the guy I'd done business with had extra information that I didn't, ie the fact that Paypal allows chargebacks.
Still, trading will be profitable in the forseeable future, but not because the trading itself is profitable, but because bitcoins are going up in value. If you're playing a +EV game, it doesn't matter how you structure the betting.