Of these, I subscribe to versions of 1, 4, 5, and 6. But let me comment first on the ones I don't agree with.
- The basic Rogoff/Reinhart observation that financial collapses due to asset bubbles just take a long time to work through. Given the size of the 2008 collapse, historical evidence suggests that it's going to take five or six years to recover, and that's that.
- The Tyler Cowen "Great Stagnation" hypothesis. We've picked through all the low-hanging economic fruit over the past century, and like it or not, we're now entering an extended period of low productivity growth because we're not inventing lots of cool new stuff.
- The related (I think) investment drought hypothesis. Ben Bernanke famously ascribed the housing bubble partly to a "savings glut" from overseas, and the flip side of that is an investment drought. The reason financial assets became so popular is that, even with all that money sloshing around the system, there simply weren't very many high-quality investment opportunities available in firms that make real-world goods and services, and that hasn't changed.
- The peak oil theory. Production of oil has pretty much maxed out, which means that every time the economy gets moving it will create a spike in oil prices, which will send the global economy back into recession. We're now in a continual oil-fueled boom/bust cycle that limits our long-term growth rate.
- The Michael Mandel contention that increased consumption simply leaks out of the economy to China and other countries. Stimulating consumption in the U.S. just won't do much for the American economy if all those extra dollars mostly get spent on overseas goods and services.
- Various structural explanations that suggest the United States has an increasing number of workers who flatly don't have the skills to do anything useful in the modern economy — a problem that was temporarily masked by the housing bubble and was only fully exposed when the economy collapsed. This takes various forms, both weak (workers can be retrained but it will take a while) and strong (forget it, they're simply useless).
- The self-serving group of partisan hack theories: regulatory uncertainty is the real problem, taxes are too high, the EPA is strangling America, hyperinflation is just around the corner, markets are cowering in fear of future deficits, etc. etc.
As a working inventor for Silicon Valley I think 2) doesn't pass the sniff test - inventors and entrepreneurs are all manically dreaming up robots, speech and vision processing algorithms, automated driving systems, information retrieval and processing systems, etc, etc: all of which will eventually be sold to corporations with an ROI calculation that basically looks at how many people would be paid how much to do the job now and then demonstrates that paying the startup for the new technology will involve a lower ultimate cost (and probably higher reliability too). Silicon Valley is currently in flat-out sprint mode - hardly a sign of nothing worth inventing or commercializing.
I think 3) is a symptom not a cause. Interest rates are low in developed countries because it's hard to grow, not the other way around. And like Kevin I see 7) as partisan rationalizations rather than genuine theories.
1) I completely agree with - historically we've seen that major leveraged booms (like the 1920s in the US or the 1980s in Japan) tend to end in tears and take a long time to recover from. Still, if that was our main problem it would be soluble by massive government borrowing and stimulus. This is roughly the Paul Krugman view of the world - that 1) is the overwhelming problem and that it could be solved if only the intransigent political system would get with the program.
However, I also subscribe to 4) - the view that energy supply is a short-term-indispensible input to economic activity and that the liquid fuel component of the energy supply is currently constrained enough that significant bursts of economic growth will quickly run into this constraint and trigger oil price shocks. We've had two of those now in the last few years (2005-2008 and 2010-2011) and I've no doubt we'll see more. These have a strong tendency to be triggers for recessions or slowdowns. To Krugmanites this is an inconvenient fact to be more-or-less ignored but to me it's a central fact of our times.
If 1) and 4) were our only problems the solution would be "Green Stimulus": a massive program of investment in alternative energy and energy efficiency measures. By having the government borrow a bunch of money and use it to subsidize plugin-hybrids, electric cars, windmills, solar panels, etc, etc we could create a bunch of jobs now in the short term while setting ourselves on course to remove our oil dependence over the course of a couple of decades. Things would probably still be very tricky in the short term: we have huge sunk investments in buildings, infrastructure, and vehicles that are organized for cheap oil and those can only be changed out slowly. In the meantime, create too much economic activity and it will still trigger an oil shock. But we'd be moving in a better direction. Not, of course, that there's any chance of the current political system delivering this, but let's keep going with what we could do if we were smarter.
So then we have the problem of 5) too. The Chinese have cheap labor, cheap capital, cheap coal, and are buying US assets to keep their currency cheap too. This causes multiple problems for the "Green Stimulus" plan - one is that because US manufacturing is struggling to compete with Chinese manufacturing, a lot of the jobs would undoubtedly leak to China. Secondly, a large scale Green Stimulus would leave the US with an even bigger sovereign debt than it would otherwise have and it's unclear to me how safe it is for an economically uncompetitive US to try to navigate coming decades with a huge public debt.
So then it's tempting to say capital controls and import restrictions (at least with respect to China). Of course the Chinese would retaliate but since they already have capital controls and they are the ones running the big surplus perhaps we stand more to gain than to lose here at present.
But then there's 6) in which I also strongly believe. In Silicon Valley, currently, it's extremely hard to hire good people because the demand for them is so strong. Decent engineers, product managers, finance people, salespeople, etc, etc are absolutely guaranteed a job. There's no question the lack of more such people is a constraint on the growth of many firms in the valley. Meanwhile the national employment/population ratio for male high-school dropouts ages 25-54 is down to 50%. The only roles I can imagine for such folks in a high-tech company is as the janitors or the guys that cut the lawn outside. There's just a very limited number of those positions (and iRobot is doing its best to eliminate the ones that remain).
So even if we could transition to a bright green economy of the future, and neutralize the Chinese threat, I'm still really struggling to see how it could provide employment, and thus meaning, to the lives of the lower percentiles of the education/intellect distribution. But without being able to do that, I struggle to see how we can have a decent society (or even a stable one).