Not to say a history PhD is useless for finding work, but its likely more difficult to find work than say a Physics PhD (which has a 96% employment rate 1st year after graduation, according to the APS[1]).
[1]http://www.aip.org/statistics/trends/reports/phdinitial.pdf
This is incorrect. It's absolutely possible to earn a humanities doctorate without going into debt (at least for the postgraduate degree(s)).
The 2011 NSF survey reports that 51% of humanities PhD graduates hold no degree-related debt, and that only 22% fund their degrees through their own resources. Compared to life/physical science students, more humanities PhDs fund their degrees by going into debt (by about 25%), but the majority of humanities PhDs graduate without debt and fund their degrees through fellowship grants and assisstantship positions, just like graduate students in STEM fields.
Anecdotally, all the humanities departments I am familiar with fund the vast majority (90%+) of their doctoral students.
I don't mean to imply a STEM major is more valuable than a History PhD either, simply that its (likely) easier to get a job after graduation. Honestly, its a damn shame the public doesn't appreciate both of these areas of work more as they are the cornerstone for improving society.
I learned a lot and pushed my theoretical understanding during my Phd, and I can not imagine being without that. However, most people is probably better off finishing off with a masters (including my former self) and getting that downpayment instead of a PhD degree.
> unless they are mature enough to consider the opportunity cost and make sounds judgements about it.
But couldn't that be said for virtually anything 20-somethings do? What about working for a startup? Or starting one? Those things involve opportunity costs too. I agree with you that it would ideal if everyone could have the benefit of wisdom and maturity before making life decisions, but that isn't going to happen. In the meantime, if you enjoy research, I say do a PhD. If you enjoy working on startups, I say do that. It's not like either of those things (provided the PhD is in STEM) are going to lead to a life of insurmountable poverty...How is it that so many students are unaware of this until the end of their education? Is it just the quintessential American "you can be anything you put your mind to" wishful thinking? This question goes doubly for humanities PhDs, because at least you can get a job elsewhere.
But that Phd in history....
I'm also acutely aware that while staying in academia would be great (despite all the bad things like crazy hours, crazy people, etc.) there is simply a very good chance it's not going to be possible, or if it is it'll be crazy competitive.
The litmus test I always think about is a colleague [postdoc] I worked with years ago. He was disgustingly smart and capable, and applied for over 100 tenure track positions before getting one. He also had an educational pedigree and publication record most of us can only dream of, and was a great guy to boot. If it takes someone like that 100+ applications what chance do the rest of us have!?
Because of this, I've taken on the rather larger responsibility of running the labs computing resources, both hardware/software. It's a lot of work (I'd estimate I spend maybe 20 hours a week doing sysadmin related tasks) but it does also give me a totally inappropriate level of responsibility which I hope will be valuable either inside academia, or in industry. I also really enjoy it, which is a nice bonus.
History - not so much.
Our society doesn't need so many history graduates. History should be a hobby, not something a million kids each year dedicate their life to.
Universities, in pursuing profits, are cutting costs. This no doubt good for their bottom line, but it might be bad for society as a whole. With the downplaying of the value of history and the humanities, perhaps people are less prepared to think outside of their narrow technical specializations.