Keynesian Stimulus: Divine Miracle or Bloodletting?

Economist Robert Barro writing in today's WSJ (emphasis added): 

"Keynesian economics—the go-to theory for those who like government at the controls of the economy—is in the forefront of the ongoing debate on fiscal-stimulus packages. For example, in true Keynesian spirit, Agriculture Secretary Tom Vilsack said recently that food stamps were an "economic stimulus" and that "every dollar of benefits generates $1.84 in the economy in terms of economic activity." Many observers may see how this idea—that one can magically get back more than one puts in—conflicts with what I will call "regular economics." What few know is that there is no meaningful theoretical or empirical support for the Keynesian position. 

If valid, this result would be truly miraculous. The recipients of food stamps get, say, $1 billion but they are not the only ones who benefit. Another $1 billion appears that can make the rest of society better off. Unlike the trade-off in regular economics, that extra $1 billion is the ultimate free lunch.  

There are two ways to view Keynesian stimulus through transfer programs. It's either a divine miracle—where one gets back more than one puts in—or else it's the macroeconomic equivalent of bloodletting. Obviously, I lean toward the latter position, but I am still hoping for more empirical evidence."