PhD is definitely a currency, and no they're not fungible: I'm trying to figure out which ones are actually worth something. In my experience it's a fairly lousy signal. Every Caltech PhD I've met has been sharp as a tack though.
The other is the hate. Especially in some industries, people are widely aware that higher education is desperately in need of reform, have had genuinely bad experiences in school, or are just plain anti-academic. In fact, the notion of "signaling" is a symptom of these problems.
Can you speak a bit more to this, and what your experience with this has been like?
It's almost like a business incubator, where they provide you with basic infrastructure, and perhaps some training, but you end up with a growing business or you don't. And in fact a lot of PhDs, at least in my field, end up becoming entrepreneurs.
You're supposed to be able to turn yourself into an independent researcher, but this is far from guaranteed. While you assume these risks, there's also the risk of getting the degree and regretting it, if the expectations (being in a leadership role, possibly directing other people) don't match with what you actually want to do, and the people skills needed for those things. And then, in some fields, you're competing with people who went straight to work after college, and have developed their careers on the job while also putting away some nice money.
Okay, enough of that. The other thing is, you can pick it up after a few months of HN, that a lot of people are really down on academia and academics. Again, this varies by field. In my field, physics, the PhD is almost the default -- there are relatively few people with masters or even bachelors degrees to be compared with, and we're also rare enough that many people have just not formed an opinion about us. ;-) Plus we do the work that most people hate, such as math intensive stuff, and we don't demand as much money. ;-)
I suggest this is an issue worth just observing for a while. There are debates among my friends about whether HN is really representative of the hive mind of the tech industry, or computer programmers, or whatever,
(or, more pessimistically, larger universities tend to have disadvantages that individual profs and departments might or might not overcome...)
There certainly are significant differences between individuals, but nearly everyone is smart and scientifically motivated.
(Many students left before graduating, maybe half, but it was only rarely because they couldn't do the work. My good friend had to leave for medical reasons, it was very sad. Another left as a sophomore. 10 years later, he asked if he could come back, and the Institute said "sure", and he graduated with straight A's. I asked him if he'd gotten smarter in the preceding decade, he laughed and said no, it just took him 10 years to get ready to work hard.)
On the other hand, most Stanford guys I've met have also been sharp, and they graduate 700 PhDs a year according to someone below.