Depends on the degree. While phds in mathematics of physics may be able to find employment as qountas at goldman and sachs what is the private sector market for degrees in the humanities, logic, philosophy, the arts, etc.
Simply because these disciplines don't directly impact the ability of apple to produce new iphones doesn't mean they are with out value and shouldn't be compensated accordingly by society at some level.
As a civilization, we probably employ more full-time professional philosophers than any other in history. We don't underinvest in the humanities; graduate students overinvest themselves in it, numerically speaking.
Humanities have always been the pursuit of the idle rich. Those without a hefty trust fund have found that they need to work to support themselves, and to find work they need skills. For those people we can only hope that their required electives provide them opportunity to expand their minds.
By the way, what did you have in mind for the means for society to compensate these non-productive people? I say non-productive because they have no jobs, thus requiring some form of compensation from society. How do you seriously propose this be done?
It's always possible to create more jobs for full-time academics. In some fields this would be a good thing--permanently employing a few hundred thousand extra physicists means we get more physics done, and physics is damn useful. In others, like philosophy, we might be reaching diminishing returns.
Simply because these disciplines don't directly impact the ability of apple to produce new iphones doesn't mean they are with out value and shouldn't be compensated accordingly by society at some level.