As someone with a PhD in a STEM field, I used to claim that if they they aren't paying you to be in graduate school, you shouldn't be in graduate school.
My niece and nephew are both, I think, currently being paid to attend graduate school (at least their parents don't appear to be providing funding and they don't have jobs outside of school), so it appears to still work.
Even in the humanities, if they really want you in the grad program, they give you a teaching assistanceship or something. Mind you, humanities assistants don't get paid nearly as well as Math assistanceships, but they do get paid.