Except that people don't get honorary PhDs or MDs. There are DLitt, DLaws(h.c.), DSci, LhD and so on. They are very carefully distinguished from earned degrees. Giving out the latter out of courtesy or for general achievement risks the accreditation of the issuing university. If you get a PhD you have taken graduate classes, done original research to a certain standard, defended your thesis, taken comprehensive exams and so on. If you have the letters M.D. after your name you've spent four years in medical school passing basic and clinical sciences, gotten a comprehensive theoretical and practical education in medicine, done a clerkship and so on. There's a world of difference between that and an h.c. diploma given at Commencement or out of respect for general academic respectability.