In the final analysis it doesn't actually matter if Leonhardt is right and some college graduates working menial jobs do get paid a little more, for no matter how much more you get paid to work the cash register or sweep floors, here is the hard reality of menial jobs and their debilitating effects on anyone with a college degree: You don’t improve your skills in these jobs, you don’t learn anything—you lose your edge. This stupefaction effect is something that Leonhardt conveniently ignores.
But menial job-induced stupefaction belies another notion widely propagated by the higher education industry—that an education lasts forever. It really doesn't, not unless you do something to keep your intellectual edge. A person with a doctorate who ends up cleaning floors is not getting better as a scholar. He is wasting his vast intellectual potential, as are the millions of his educated compatriots in menial jobs. In fact, at most, a graduate probably retains his knowledge and intellectual ability for only a few years after graduation. Unless he uses his degree and his intellectual activity at work and reinforces his knowledge, he will soon forget what he has learned. A graduate who is forced to work a menial job will in a few years be reduced to the same intellectual level that he was at before he started college. Knowledge, creativity and intellectual prowess are fluid—to maintain them you have to have the kinds of jobs that challenge those faculties and reinforce them. And for this loss of one's intellectual capability the slightly higher wages in menial jobs hardly compensate. Even if an education were to last a lifetime, however, this would be small comfort to someone working at a cash register in a company that does not promote based on educational achievement.
Ultimately Thiel was right in calling a college education speculative for the simple reason that most employers do not value a degree in and of itself. And the intellectual benefit obtained by getting a degree dissipates unless it is reinforced in a suitable job. Consequently, a college degree offers returns only for those who because of their other, special qualities are able to get work commensurate with their training immediately after graduation; only they will see returns on their investment. Anyone else will most likely incur a huge loss: not only will their forget what they've learned, they will be saddled for the rest of their lives with thousands, sometimes tens of thousands of dollars in student loans which their hand-to-mouth menial job wages will never repay.