Typically only Doctors have those kind of student loans that are justifiable. I don't even know if science phd's are that justifiable unless you're doing some shyt that has some real potential for the future like machine learning or something.
Overall, I'd say there are very few scenarios in which that type of debt is worth taking on.
Medical School: you have a guaranteed 25+ year window of six-figure annual earnings to pay down the debt.
T-5 Law School: Yale, Stanford, Harvard, etc. Somebody will pay you $100k to do something, even if unrelated to law!
T-5 Business School: Harvard, Stanford, Wharton, etc. You'll make $100k and probably get good bonuses, depending on industry.