Mark Greenberg, an earmark lobbyist, argues for earmarks

I fear the unintended institutional consequences of an earmark ban. If we curtail Congress's constitutional prerogative, reduce its power relative to the presidency and further fragment our politics, our political system will suffer.

From the Washington Post

Update: Jacob T. Levy argues against Mr. Greenberg's argument that banning earmarks doesn't affect spending.

First, it is more expensive to do things inefficiently than to do things efficiently. Building the Ted Stevens Bridge To Nowhere or the Robert Byrd Gold-Plated NORAD Auxiliary High Command Of West Virginia means that money has simply been wasted, and that all the needs that weren't met this year will arise again next year.