Speculation is fine for commodities, because it helps the market determine the price.  It's terrible for fledgling currencies.  There's a reason that new currencies have traditionally been backed by something else (gold, other established currency, etc.):  you want people comfortable that the value is based on something other than people's perceptions and you won't get screwed if you hold on to them in exchange for goods and services.  Otherwise, why would anybody use the new currency?  This problem is magnified tenfold for Bitcoin, since it's not backed by any institution and has a much higher barrier to entry for the casual user than little slips of paper with numbers and pictures of dead people on them.