Futures exchanges exist to provide vital liquidity to commodities markets. Without futures exchanges, there would be drastic and frequent price fluctuations in our commodities and the goods made from them. Businesses that produce / use these commodities would have to pass those fluctuations through to the consumer immediately (or at least within their credit floats), the net result being that the price of gas (or any other commodity) would fluctuate by very large amounts very often.
Speculators bear all that risk of price fluctuation in the interim between production and delivery and create the liquidity needed for businesses to lock in the sales price of a good they haven't yet produced (or the purchase price of a good they need to use in production). Without futures exchanges, and the speculators that keep them moving, businesses would have no way to plan production.
The futures markets are a zero sum game (less the vig, of course). For every contract that someone is long, someone else has to take the other (short) side. Many, many more (think 100:1 or more) futures contracts for goods exist than actual goods traded.
If as a speculator, I buy a contract to purchase gold, for instance, at $1200/oz. in November, I'm betting that gold will be more than $1200/oz. by November. If it is, I can take delivery of the gold and sell it on the market at the spot (immediate delivery) price. If I'm wrong, and I take delivery, I will either keep it in a vault, or sell it at a loss.
In practice, speculators do not take (or make) delivery. They either liquidate their position before contract expiry or the exchange will settle their accounts against the opposite positions for cash. If you, as a speculator, hold through expiry, there is a chance you will have to take (or make) physical delivery, so in practice all speculators close out their positions prior to this. The only ones left standing, so to speak, are the actual producers and consumers, though they probably never dealt directly with each other.
Futures markets don't really move the market, though they do influence it. The markets are a way for producers and consumers to hedge (i.e. pass their risk on to speculators). The real market is the spot price of a commodity on any given day. Futures markets smooth the fluctuations in the market price out. Supply (OPEC, lack of refineries, regional blends of gasoline) and demand (from China, India, summer driving season, etc.) are what really move the oil and gas markets.
Futures markets exist almost entirely to provide hedging opportunities to producers and consumers, and to do this the markets need speculators. Lots of them.
This notion that speculators are bad for commodities markets and should be removed or reined in, is the polar opposite of the truth. "Speculators" are a convenient scapegoat for the media and politicians, and this finger pointing works because of the criminal negligence that exists in our education system that refuses to teach anyone anything not related to learning how to be a wage slave.
As far as oil as a bubble market at the moment, I don't know but I would say we are probably above the true value curve. I don't believe this enough to put my money where my mouth is, however.
I am certain that the trend in oil is up and is going to remain up due to increasing demand from the 2nd world and the general resistance toward alternative energy solutions such as nuclear power, wind, hydroelectric, domestic drilling, etc. professed by the NIMBY and Green crowds.