Great post with a lively comment thread at Chemjobber here:
Chemjobber's main point is that graduate school has an opportunity cost: you could have spent those 4-7 years doing something else, and maybe that "something else" would actually have created more value for you. A commenter on the thread named Janet makes a point that I rather like:
"...the very best reason to pursue a Ph.D. in chemistry is because you want to learn what it is like to build new knowledge in chemistry in an academic setting... since [getting a job] is a crapshoot... If you don't want to learn about this knowledge-building process -- and want it enough to put up with long hours, unrewarding pay... and the like... then possibly a Ph.D. is not the best way to spend 5+ years of your life."
A couple people on the thread referred to this philosophy as "education for its own sake," but what it really is is placing another necessary condition on pursuing a particular degree. It should build value for you, and (considering the costs) you should want it for its own sake, too. If you don't really want to learn the material and the process -- if the only thing driving you forward is the hope for prestige or money or some intangible reward attached to the job you hope to get -- what kind of a chemist are you going to be, anyway? Assuming you do get a job.
As for me, I got my engineering Ph.D. entirely on the taxpayer's dime (though not without opportunity cost, which falls somewhere on the spectrum between death and taxes), and despite having no job at all I persist in the hope that when it is all said and done it will have been an experience that added value to me, in the "liberal arts tradition" -- the experience made me a more well-rounded person and equipped me with a number of skills that I appreciate. I certainly gained some tangential benefits that I could not have expected, through the personal connections and friendships I made during those years. At the very least I learned at the visceral level that what I really wanted to do during my thirties was stay home and care for my children.
(Whether it was a good deal for the taxpayers is up for debate, but I didn't sign any papers that said "thou shalt repay the NSF by valuing your career over your sanity and your family's comfort and ease" so I figure it was their fault for not spelling that out when they offered me the fellowship.)
There are more good insights over there, so I recommend the article and the comment thread especially to my readers who've done time in graduate school or considered doing it, as well as anyone interested in educational philosophy.