In other words, even if the US were to provide the resources to make these people economically valuable, would there be jobs for them?
[WS:] So if you believe that there are no jobs available, how do you explain the undocumented immigration to the US in search of jobs? It stands to reason that there must be jobs available, if people abroad are taking considerable risk and cost to come here to work, no? So it follows that these jobs are also available to the domestic population, which demonstrates that structural joblessness is an unlikely culprit of high incarceration rate of the US population.
I agree with Jordan on this - high incarceration is caused by high crime rates and a relative efficiency of the US justice system vis a vis many other countries, like for example Russia. I also believe that the causes of those high crime rates are social rather than economic, especially the proliferation of violent subcultures, cult of violence, and easy access to guns.
Another observation - comparing unemployment rates in the US and EU can be a bit tricky, because it is a bit like comparing apples and oranges. On the US excludes more people from the definition of unemployment, on the other hand the EU includes more in e.g. people who work under the table and claim unemployment benefits. Since EU unemployment benefits tend to be more generous than those in the US, I strongly suspect that a far greater number of Europeans than Americans belong to the second category.
Wojtek