As someone at the end of this process, I read this sort of discussion about the value of a PhD with some dark sense of humor. There are two things to say about this, I suppose:
1. Getting one's PhD isn't necessarily a miserable experience; but it's also not necessarily an enjoyable one. It's true, certainly, that I set my own research agenda, which is nice. This does not mean I get to read what I want. If anything, it means I spend my time mastering the literature about my preferred subject, and the quality of that work is uneven. I've had my fill of articles and books discussing whether Grotius' etiamsi daremus means he's introducing a brave new world of secular, humanist political theory, or simply recycling a late scholastic rhetorical trope. But it must be done if I am to defend successfully.
The key point which the whole 'life of the mind' thing misses is that a PhD is professional training. It is work. Like any other kind of work, sometimes you'd rather be doing something else. Like any other kind of work, you make a choice about how much you want to do this particular activity, and what you're willing to sacrifice to make that happen. Some days, the PhD looks like a very smart route, and the only thing I could be fit for. Others, I envy the people who can just forget about their work when they get home (and not, say, have an hour-long dinner conversation about the structure of one of their chapters). If you think it's "have fun, do what you love, go to Europe every once in awhile," well, it's work. This means drafting and re-drafting and having your carefully constructed arguments blown up by one well-placed observation by your adviser.
2. However much knowledge you might think you have about the market, with placement statistics and several years of watching cohorts above yours go on the market, you know basically nothing until you try it out. What you learn is, as Dan Drezner said some time ago, that the academic job market is globally rational but locally capricious. You should never take any one rejection too seriously, because it's too difficult to know what it means: you might have been taken out of consideration for something you didn't even realize would be a problem; you might be candidate #6 when they only phone-interviewed five people. "Locally capricious," however, is a lot more difficult to withstand when you get four such rejections in the space of two days, and it's very hard not to read it as a personal rejection, no matter how clear the facts are in your head.
It's for something like a combination of these two reasons that I generally advise the few people who ask not to go to grad school. I say this, also, as one of the lucky ones: I have a postdoc offer for next year, from a program you might have heard of at a university you have definitely heard of, in a bad year on the job market. But getting a PhD without at least the intention of teaching and doing research makes as much sense as going to law school if you don't want to be a lawyer.