Speculators earn a profit by absorbing risk that others don't want. Without speculators, investors would find it difficult to quickly hedge or sell their positions.
Speculators also provide us with information about the fundamental values of investments. When the fundamentals appear favorable, they buy. Otherwise, they sell. If their forecasts are correct, they profit. This causes prices to more accurately forecast an investment's value, spreading useful information. For example, the clearest evidence that Greece has a serious debt problem was the run-up of the price for buying CDS protection against the country's default.
Is this sort of speculation wrong? I have not heard why.
Those who call for stamping out speculation may be confused between speculation and market manipulation. Manipulation occurs when investors "attack'' a financial market in order to profit by changing the value of an investment. Profitable speculation occurs when investors accurately forecast an investment's fundamental strength or weakness.
An example of manipulation is an attack on a currency with a fixed exchange rate in an attempt to cause a devaluation of that currency. Mr. Soros allegedly attacked the British pound in 1992 and the Malaysian ringgit in 1997. An attack on the equity or CDS of a bank could create fears of insolvency, leading to a bank run and allowing the manipulator to profit from his attack.
In the week of Lehman Brothers' bankruptcy in September 2008, John Mack, then CEO of Morgan Stanley, suggested that the difficulties facing his firm stemmed from such an attack. But firms complaining of unfounded short-selling often had real problems beforehand.
A market manipulator can also attempt to profit by "cornering" a market. This is done by holding such a large fraction of the supply of an asset that anyone who wants to buy that asset is at the mercy of the corner holder when negotiating a price.
The market for silver was temporarily cornered in 1979-80, when Nelson Bunker Hunt and his brother William Herbert Hunt held silver derivatives representing approximately half of annual global silver production. In the end, the Hunt brothers were unable to maintain a corner. As they sold, silver prices fell, causing them calamitous losses.
Market manipulation for profit is not easily done. If the fundamentals of supply and demand suggest that the value of something is $100, then a manipulator must buy at prices above $100 in order to drive the price up or to accumulate a monopolistic position. He then owns an asset that on paper could be worth more than what he paid for it. However, he must sell his asset in order to cash in on his profit. This spurs the price of that asset to fall, as the Hunt brothers learned.
Simply driving up the price, as speculators are alleged to have done in the oil market in 2008, is not enough. To make a profit, a manipulator needs to obtain monopolistic control of the supply. Given the size of the oil market, that seems implausible, absent a major and sustained conspiracy.
In the United States, trade with an intent to manipulate financial markets is generally illegal. Regulators should keep anti-manipulation laws up to date and aggressively monitor potential violators.
Speculation is not necessarily harmless. If a large speculator does not have enough capital to cover potential losses, he could destabilize financial markets if his position collapses. The Over-the-Counter Derivatives Markets Act, which could come up for a vote in the Senate soon, will hopefully reduce such risks.
It would be better for our economy to enforce anti-manipulation laws, and require that speculators have enough capital to cover their risks, than to attempt to squash speculation.
Mr. Duffie is a professor of finance at Stanford University's Graduate School of Business.