The problem in humanities is that the market is saturated, also, the majority of undergraduate classes are taught by graduate students (they're cheap!), further reducing the number of potential hiring positions.

So you have to actually be exceptional and have published something interesting to even have a good chance at making it as a professor.

You could do other things as well, write books or work for various foundations (teach high school!), but you can do those things without a Phd in medieval English literature.

You also are spending 8+ years not getting paid or putting yourself into debt, and that you still might end up working at Arby's (or what have you).

He left out that the pay for a starting professor sucks. (Considering that you just spent 8 years of your life getting the degree).

Computer science is a bit of a different ballgame in that it is applicable (well, vaguely) to software development. So you might be able to get a job that is orthogonally relevant to whatever it was that you passionately studied in graduate school.

The sad truth, however, is that the majority of software development does not come anywhere close to requiring a Phd. And you still come out up to your eyeballs in debt or flat broke. The good thing about it is that it looks pretty good on a resume. (Although weighing 8 years writing software against 8 years in grad school, I might go with the guy who has work experience... is kind of a toss up).

The google/ibm/microsoft research positions are few and far between, in any event.