It was the British economist John Maynard Keynes who famously wrote that ideas, "both when they are right and when they are wrong, are more powerful than is commonly understood. Indeed, the world is ruled by little else." Right now, I'm worried about the damage that might be done by one particularly wrong-headed idea: the notion that, in stark contrast to Keynes's teaching, government spending destroys jobs.

No, that's not a typo. House Speaker John Boehner and other Republicans regularly rail against "job-killing government spending." Think about that for a minute. The claim is that employment actually declines when federal spending rises. Using the same illogic, employment should soar if we made massive cuts in public spending—as some are advocating right now.

Acting on such a belief would imperil a still-shaky economy that is not generating nearly enough jobs. So let's ask: How, exactly, could more government spending "kill jobs"?

It is easy, but irrelevant, to understand how someone might object to any particular item in the federal budget—whether it is the war in Afghanistan, ethanol subsidies, Social Security benefits, or building bridges to nowhere. But even building bridges to nowhere would create jobs, not destroy them, as the congressman from nowhere knows. To be sure, that is not a valid argument for building them. Dumb public spending deserves to be rejected—but not because it kills jobs.

The generic conservative view that government is "too big" in some abstract sense leads to a strong predisposition against spending. OK. But the question remains: How can the government destroy jobs by either hiring people directly or buying things from private companies? For example, how is it that public purchases of computers destroy jobs but private purchases of computers create them?