Should dropping out of a PhD program be treated the same way as quitting a regular, industry job?
This answer addresses the idea that the work a PhD student does is just like work at another job, and therefore quitting the jobs should be viewed the same. (My answer suggests that it should be unusual for people to enroll and then quit without there being a serious problem, and also that potentially elements of society might place stigma on that action to keep people from wasting educational resources.) There also seems to be an indication in the question that people should be free to casually start positions as Ph.D. students without the intention to finish the degree. (I may be overstating the poster's view, but that extreme version is what I address below.)

I believe that for an individual, leaving a program or leaving academia can be the right choice for all involved, and that work as a graduate student is valid work experience to list on a resume. However, it is harmful in the long term if people enter graduate school without the intention of completing the degree.



A huge part of the compensation for being a PhD student is funding one's classes, training, library access, access to lab materials, potentially travel funding, and access to smart peers and smart professors. It costs a lot to create a learning and research environment.

For instance, a postdoc working a similar job in a lab will get paid more; partly because they need less supervision and training, have more experience, and have more responsibility, but also because the professor does not have to fund the tuition and student benefits for that postdoc. And a professional lab worker should be paid even more.

If, as you say, being a PhD student is just another job, then people who do not value all of the parts that support academic success could value those things at zero and realize they are getting a very poor wage. They could work at a private lab for the same work--but without the support for learning and autonomous research--and get paid much more for the same style of tasks.

Again, it costs a lot to create a learning and research environment, and universities are investing in their students' success. Hoxby has a model of university funding that likens university founders (and later donors) to venture capitalists investing in human capital and in research: http://www.nber.org/papers/w18626.

As Hoxby writes: "Because some of the students' returns will presumably be social, the obligation on them can be multifaceted.  Those who earn private returns on their human capital can be asked for gifts in the form of money. Others could be asked for gifts in the form of expertise. Others could be asked to use their political influence to sure that the university is treated well by the government.  And so on." Hoxby 2012, p. 19 

If people are taking Ph.D. positions as mere jobs, they are less likely to fully contribute to the educational environment, less likely to take full advantage of the costly investment in their educational environment, and less likely to give back to the institution to help it sustain itself.



TL;DR: It is extremely short-sighted to think that students are merely workers. It is to academia's detriment if students, professors, schools, and governments act as if they are.

(These models and my thinking are largely based on the U.S. system, which the poster addressed. I would be interested in thoughts on how this compares to other funding models.)



Note: I do not intend this answer to say that grad students are or are not employees for the purposes of unionization or other purposes. However, I believe this account of why schools fund tuition for advanced students as an uncertain investment helps us understand why the rebated tuition should not be taxed as regular income (as a recent US tax plan suggested doing).