WASHINGTON (MarketWatch) — Everyone from the right to the left agrees that job growth is far too weak. But what they can’t agree on is what’s causing this jobless emergency, or what to do about it.

On the left, commentators generally point to cyclical problems in the economy, particularly the slow growth in spending (what economists refer to as aggregate demand). Their argument is that businesses aren’t hiring more workers because the demand for their goods or services isn’t growing fast enough to force them to hire more workers.

It’s a Keynesian view, and it largely fits the facts, as I argued in my columns of May 17 and of May 31.

The classic way to get more demand in the economy is to lower interest rates to encourage more borrowing and more spending. But the Federal Reserve has already cut interest rates as much as it can, and it’s doing a lot of unorthodox things like buying bonds to achieve the same result: Create more spending.

The Fed is doing what it can, but it’s not enough to ignite the virtuous cycle of increased spending, income and jobs that those 20 million unemployed Americans need.

The right says labor is too expensive, but the data show labor costs are growing very slowly. MarketWatch

Is there another way to boost demand? Sure, when there are lots of idle resources (labor, unused productive capacity and capital), the government can increase demand by spending more on its own account, or by giving the people some extra money (tax cuts or food stamps, for example) to spend as they wish.

Unfortunately, the government hasn’t been doing that. After a burst of stimulus in 2009 and 2010, federal, state and local governments have been doing less, not more. This drives commentators on the left crazy.

For example, Princeton economist Alan Blinder argued this week at the Roosevelt Institute’s conference on the jobs emergency that the clamp down on government spending has cost us about 3 million to 4 million jobs. The unemployment rate would be below 6% if government spending had merely increased at the same rate it did after the recession in the early 1980s under the sainted Ronald Reagan.

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On the other hand, the right’s explanation for our jobs emergency comes from a totally different dimension. The right tends to focus on structural problems in our economy that prevent businesses from hiring, things like taxes, regulations, and the costs of hiring additional workers.

For instance, MarketWatch columnist and Manhattan Institute fellow Diana Furchtgott-Roth argued at that same Roosevelt Institute forum that business aren’t hiring because labor costs too much.

Read Furchtgott-Roth’s column: 4 ways the government is discouraging hiring.

Most of the points made by the right are perfectly valid: We should eliminate inefficient taxes and regulations and reduce the cost of hiring as much as we can (but the devil is in the details).

However, the structural explanations don’t actually explain our problem: Why is hiring slow now? After all, businesses always face taxes, regulations and other costs of doing business, but that didn’t keep them from growing their businesses in other times.

What makes this period different from the others? It’s not that taxes are higher now; they aren’t. The fastest job growth in the post-war era came in the late 1970s when the top corporate tax rate was 48%, instead of the 35% that prevails today. The second highest job growth was in the early 1950s, when the statutory rate was 52%. Read more about taxes and growth.

Individual tax rates are also much lower now than they were during periods of more robust growth.

The right says small businesses can’t get credit, but the data show banks are lending again. MarketWatch

What about the regulatory burden? Has it grown? The right almost always cites the Dodd-Frank financial regulations and Obamacare as examples of burdensome regulations that stifle growth. But have these two signature laws really had an impact? Not that we can see.

Dodd-Frank is supposedly squeezing credit for smaller and mid-sized firms. But business lines of credit (commercial and industrial loans) have actually grown quite a bit in the past two years, rising at an annual rate of nearly 14%, about as fast as they grew in the late 1990s and in 2006 and 2007. And it’s not just big banks that are lending; C&I loans from small U.S. banks have risen at an 11.5% annual pace.

What about Obamacare? It hasn’t been fully implemented yet, so companies don’t really know how it will affect them. There is some uncertainty. But companies know they won’t have to provide health insurance to part-time workers, so they could avoid the burdens of Obamacare simply by hiring part-timers or by giving more hours of work to the people already on their payrolls.

So far, average hours haven’t increased, and bosses haven’t been loading up on part-timers. Almost all of the job growth over the past two years has been in full-time positions, not part-time ones.

What about the cost of labor? Has it exploded as Furchtgott-Roth argues? No, it hasn’t. Inflation-adjusted compensation per hour is up just 0.3% in the past year and is up just 0.5% in the past five years. Including both wages and benefits, labor is nearly as cheap today as it was in 2008.

When you factor in productivity gains, labor is even cheaper than it was back then.

Other structuralist arguments favored by the right also fall apart under examination. Most structural impediments to hiring fall unevenly on different companies, industries, geographies, sectors or sizes of firms.

If structural burdens were harming some companies disproportionately, you’d expect other companies to rush in to grab market share. If small companies can’t grow because credit is tight or because labor costs are too high, you’d expect larger companies to steal their customers.

But the data show that hiring is weak at large corporations as well as small firms, at lightly taxed companies as well as heavily taxed ones, and at lightly regulated companies as well as heavily regulated ones, just as the Keynesians predict.

The right and left have different stories to explain our jobs emergency. The story from the left fits the facts, but the other one sounds like a fairy tale.