James Surowiecke in the New Yorker magazine says:

Furthermore, the ban on online betting is hindering the development of new markets that could predict far more important outcomes than that of the N.B.A. finals. In the past few years, a host of prediction markets, as they’re usually called, have appeared online, offering people the chance to speculate on subjects ranging from the box-office performance of Hollywood films to the outcome of Presidential elections and the spread of bird flu. These markets’ forecasts have proved remarkably accurate—just as bettors collectively do an exceptionally good job of predicting sports results. (In 2004, for instance, Tradesports, a Dublin-based prediction market, called thirty-three out of thirty-four races in the Senate correctly, and called all fifty states correctly in the results for the electoral college.) But in the U.S. these markets have to use play money, because using real money would constitute gambling. The online gambling ban prevents these markets from getting bigger and more accurate.

That might seem an acceptable cost if the war on Internet betting looked set to accomplish its goals. Instead, it’s likely to make the problems it was designed to solve worse. Online bookmakers have been portrayed as shady operators, but the biggest of them are far more transparent and easy to regulate than illegal bookies, many of whom have ties to organized crime. David Carruthers, before he was arrested, had been actively calling for the regulation of his industry. Congress may think that driving bettors back underground can curb underage gambling and money laundering, but don’t bet on it.

Read the whole thing (hat tip to Don Luskin).

I have made similar arguments here about the law. And here is a good WSJ article on current enforcement.

I've also quoted some smart dudes who agree. And I have talked about the benefits of predictive information markets.