Ah, good - I've been meaning to do something like this myself, but never got around to it. Jeff Frankel sorts speculation into three types and notes that only one of the three types, "bandwagon behavior," is worrisome. However, there's little evidence that this type of speculation is present in commodities markets:
Commodity Prices, Again: Are Speculators to Blame, by Jeff Frankel: ...Many currently are trying to blame speculators for the high prices of oil and other mineral and agricultural products. Is it their fault?
Sure, speculators are important in the commodities markets, more so than they used to be. The spot prices of oil and other mineral and agricultural products — especially on a day-to-day basis — are determined in markets where participants typically base their supply and demand in part on their expectations of future increases or decreases in the price. That is speculation. But it need not imply bubbles or destabilizing behavior.
The evidence does not support the claim that speculation has been the source of, or has exacerbated, the price increases. Indeed, expectations of future prices on the part of typical speculators, if anything, lagged behind contemporaneous spot prices in this episode. Speculators have often been “net short” (sellers) on commodities rather than “long” (buyers). In other words they may have delayed or moderated the price increases, rather than initiating or adding to them. One revealing piece of evidence is that commodities that feature no futures markets have experienced as much volatility as those that have them. Clearly speculators are the conspicuous scapegoat every time commodity prices go high. But, historically, efforts to ban speculative futures markets have failed to reduce volatility.
One can distinguish three kinds of speculation in the face of rising prices. First, there is the “bearer of bad tidings”... The news that, in the future, increased demand will drive prices up is delivered by the speculator. Not only would it be a miscarriage of justice to shoot the messenger, but the speculator is actually performing a social service, by delivering the right price signal that is needed to get real resources better in line with the future balance between supply and demand. Without him, the subsequent price rise would be even greater, because supply would be less. But it does not appear that speculators played this role in the commodity boom that started earlier this decade: as already mentioned they, if anything, lagged behind the spot price.
Second, when the price is topping out, stabilizing speculators can sell short in anticipation of a future decline to a lower equilibrium price. This type of speculator again adds to the efficiency of the market, and dampens natural volatility, rather than adding to it.
Third, in some case, when an upward trend has been going on for a few years, speculators sometimes jump on the bandwagon. Market participants begin simply to extrapolate past trends and self-confirming expectations create a speculative bubble, which carries the price well above its equilibrium. Examples of previous bubble peaks include the dollar in 1985, the Japanese stock and real estate markets in 1990, the yen in 1995, the NASDAQ in 2000, and the housing market in 2005.
It is the third kind of speculation, the destabilizing kind (also called bandwagon behavior or speculative bubbles) about which politicians, pundits, and the public tends to worry. There is little evidence that this has played a role in the run-up of commodity prices. So far, that is. Just because the boom originated in fundamentals does not rule out that we could still go into a speculative bubble phase. The aforementioned bubbles each followed on trends that had originated in fundamentals (respectively: rising US real interest rates, 1980-84; easy money and rapid growth in Japan, 1987-89; US recession, 1990-91, and Japanese trade surpluses; the ICT boom in the late 1990s; and easy US monetary policy after 2001). It could happen yet in commodity markets.