I would disagree, given what we know about the economic conditions here and around the world. I think declining participation is, in fact, a significant sign of economic weakness with nothing but bad effects likely to follow from it.
And if it doesn't hold true? If inflation-adjusted GDP grows slower than the population the net economic effect is still negative and we have not yet recovered ground lost in this area since the recession. This is what people mean when they describe the recovery as anemic.
See above. Per capita GDP must outpace inflation and population growth for this assumption to hold value. This is not true in many European economies, for example, despite nominal GDP growth.
That's another debate (and a highly ideological one) and not directly consequential to this one.
No, you misunderstand the argument. The argument is predicated on the idea that people who cannot find a job for [6 months|1 year|3 years|whatever] get discouraged and stop looking, not that they're just lazy welfare bums. The argument is that economic conditions are worse than the blanket "unemployment rate" makes them appear, because it doesn't count anyone not actively seeking employment because it assumes anyone who wants to earn wages is looking for a job. This is partially due to the very long established trend of ever-increasing economic participation in the U.S. I think this is undeniably true and anyone denying it is either willfully deceptive or has their head buried in the sand. Now, quantifying exactly how much worse the economy is at present than the unemployment rate indicates is nearly impossible and deciding where to apportion the blame for it is even more difficult (and will pretty much always come down along the lines of your pre-existing sympathies).
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"Rather than being the result of demographics or choice, the rise in the number of people who are not actively looking for work is in substantial part the result of low demand for labor, according to a new study by David Blanchflower and Adam Posen, both of whom are former members of the Bank of England's rate-setting Monetary Policy Committee.
[...]
As a result the Fed has moved to a far more complex data set to use to help set forward guidance of when it might eventually raise interest rates.
Not only will it look at the unemployment rate, but also the change in the participation rate, job turnover, wage growth and long-term unemployment, among others."
http://www.reuters.com/article/2014/...A3L07B20140422