A doctor or dentist wanting to switch to flying is one thing... sunk costs are already sunk. The cost of flying at that point is just the cost of flying, plus lost opportunity cost during the lean years (more significant for an MD/DDS than for say a career-changing accountant).
Telling some-one who is pre-med or pre-dental school to do that and THEN go fly really does not make sense at all.
Years past, I would have encouraged folks to get a degree is something useful and portable, as a backup job. But back then you needed the degree anyway, a little more time and money to get certified in say accounting wasn't a ludicrous proposition. But today you don't even need a degree to fly (for the time being at least), you can quickly rise above the furlough high-water mark, most US airline pilots work for a comapny which is too big to fail, and they all have pretty good LTD programs. At this point if you want to fly, go fly, and do it quickly so as to grab as much seniority as you can while the retirement wave is still playing out.