There's nothing wrong with trading Bitcoins, just like there's nothing wrong with exchanging USD to EUR to buy a glass of wine.
Yes, but if you are spending a lot of time or effort trying to make money on an essentially unproductive activity
Speculating can be a productive activity,
if done right, that is, if speculators manage to guess correctly the future price movements. A speculator that make mistakes in such guesses make things slightly worse, though. Obviously, nobody has more incentives to make it right than the speculator himself.
http://www.thefreemanonline.org/columns/the-benefits-of-speculation/http://wiki.mises.org/wiki/SpeculationThat's just part of a more general rule actually. If you study praxeology and economic science you'll understand that any activity that brings profit without violating any property right (directly or indirectly) is productive.