What about people in upper-middle-class office jobs who spend the vast majority of every day in their office browsing Reddit?
What about people who do work, but who go into their workplace with a terrible attitude and end up failing to provide the service customers pay for?
These are three types of people that you can also observe, if you look hard enough, and they are not always destitute. They also (arguably) don't work - just having a job or money in the bank doesn't mean you contribute your fair share to society. Granted these observations alone, which are just as hard to quantify as the Krugman quote above, it's hard to say that the war on drugs (or the war to put poor people into prison, whichever name you prefer) does not exploit lower-class people. If there are always people who don't work as much as others would like them to, there's nothing theoretically different about people born into different social strata.
So, the Krugman quote above is almost reprehensible, and I also don't believe it's backed by data. For instance, a full-time federal minimum wage worker makes $15,080 a year. This is enough to live above the poverty line if you only support yourself, but not even close to enough to support a spouse and even one child (http://poverty.ucdavis.edu/faq/what-are-annual-earnings-full...). How can you possibly say that people who try and support their families on a minimum wage salary are mostly lazy bums who don't work?
I would like to see how Krugman backs up his argument. Data is always welcome.