Who shouldn't go to college and end up with huge debt?

Judith Scott-Clayton asks over at Economix who should not go to college:

While college may be a great investment, it’s not like investing in the stock market: a prospective student can’t just fork over some money and let someone else worry about how to make it grow. For college to have any payoff, students must participate in the process by going to class and engaging with course materials, peers and instructors.
The cost of college includes not just monetary costs but psychological costs, which are highest for those who either strongly dislike classroom instruction or have to work particularly hard to get anything out of it. Individuals with high psychological costs who enroll anyway because that is what they believe they “should” do may end up with the worst of both worlds: forgoing income (and possibly accumulating debt) without accumulating skills. 

The downside to all this?  Student debt that now has hit the trillion dollar mark, and worse:

we've reached a point where two-thirds of college seniors now graduate in debt, where a total of 37 million Americans now owe money on their education. Sixty-seven percent are between the ages of 18 and 39, but recent research suggests the fastest growing group of borrowers may be in middle age -- people who have been laid off from jobs or are afraid their professional skills aren't fresh enough to keep up with a changing economy. [...] For young graduates -- or dropouts, for that matter -- the debt will drag on their finances well into adulthood. For the adults, it's an investment they may not have a time to recoup. Many are already being overwhelmed by what they owe. The NY Federal Reserve believes that more than a quarter of all borrowers with due loans are now delinquent on some of their payments.