Right now the weaponized Keynesians are out in full force — which makes this a good time to see what’s really going on in debates over economic policy.

What’s bringing out the military big spenders is the approaching deadline for the so-called supercommittee to agree on a plan for deficit reduction. If no agreement is reached, this failure is supposed to trigger cuts in the defense budget.

Faced with this prospect, Republicans — who normally insist that the government can’t create jobs, and who have argued that lower, not higher, federal spending is the key to recovery — have rushed to oppose any cuts in military spending. Why? Because, they say, such cuts would destroy jobs.

Thus Representative Buck McKeon, Republican of California, once attacked the Obama stimulus plan because “more spending is not what California or this country needs.” But two weeks ago, writing in The Wall Street Journal, Mr. McKeon — now the chairman of the House Armed Services Committee — warned that the defense cuts that are scheduled to take place if the supercommittee fails to agree would eliminate jobs and raise the unemployment rate.

Oh, the hypocrisy! But what makes this particular form of hypocrisy so enduring?

First things first: Military spending does create jobs when the economy is depressed. Indeed, much of the evidence that Keynesian economics works comes from tracking the effects of past military buildups. Some liberals dislike this conclusion, but economics isn’t a morality play: spending on things you don’t like is still spending, and more spending would create more jobs.

But why would anyone prefer spending on destruction to spending on construction, prefer building weapons to building bridges?

John Maynard Keynes himself offered a partial answer 75 years ago, when he noted a curious “preference for wholly ‘wasteful’ forms of loan expenditure rather than for partly wasteful forms, which, because they are not wholly wasteful, tend to be judged on strict ‘business’ principles.” Indeed. Spend money on some useful goal, like the promotion of new energy sources, and people start screaming, “Solyndra! Waste!” Spend money on a weapons system we don’t need, and those voices are silent, because nobody expects F-22s to be a good business proposition.

To deal with this preference, Keynes whimsically suggested burying bottles full of cash in disused mines and letting the private sector dig them back up. In the same vein, I recently suggested that a fake threat of alien invasion, requiring vast anti-alien spending, might be just the thing to get the economy moving again.