I don't think it's the same question - the function of a PhD for science researchers is very different from the MD/residency for surgeons, which is actually ver

I don't think it's the same question - the function of a PhD for science researchers is very different from the MD/residency for surgeons, which is actually very different from the function of a JD and the Bar for lawyers (lawyers don't go through anything like the apprenticeship a surgeon goes through to become licensed, and a PhD generally doesn't provide a license to do anything). Also, keep in mind that many people believe that the Bar and AMA are actually large scale cartels that do more to harm the public than good. This isn't necessarily an argument that credentials and licensing are bad per se, it's an argument that the scarcity of services causes more damage than the dilution of talent (for instance, nurse practitioners might be able to provide a very high level of service in areas where MD's currently enjoy a monopoly). I'm one of the folks who are frustrated with the cartel-like behavior of professional associations in the US (and elsewhere), but there's obviously a wide range of opinions on the subject - some think they should be essentially abolished, others think they are fine in principle but need to be reigned in to ensure that "protecting the public" doesn't morph into "protecting the cartel." It's controversial, of course. But you might be interested in reading Milton Friedman's essay on the licensing of Medical professionals (just google for it, you'll find it quickly). Regardless of whether you agree with it, you'll probably find it interesting.