Actually, it is a pursuit for the individual but a product for society. Ultimately, there exist two productive paths for a newly minted PhD - either join academia or enter the workforce. Both paths are governed by the laws of supply and demand. Ergo, it is possible to over-produce education, from the point of view of society.
For sustained survival. It is reasonable to assume that anyone who decides to do a Phd is motivated to explore the depths of a topic and push the boundaries of human knowledge. However, that knowledge has value only in the scope of the world we live in. This value is governed by society, by us, and manifests itself as research grants, job opportunities etc. So one needs to consider this IF one wants to be productive (by doing a PhD). And of course, the whole point is void if one does not want to be productive, ergo, is not interested in his sustained survival.
This is a general observation. I don't see why it should be mostly about American society.
