Once upon a time, physicians had a great idea: get the government allow a group of them to control licensing for their profession. By restricting their numbers, they could keep their own salaries higher. Initially, this worked pretty well (for their members), and the arguments were palatable for consumers: Do want someone with no formal medical education cutting your abdomen open and rummaging around inside?
Other professions caught on, of course, sometimes to comical effect: Do we really need to license nail painters or foot massagers? Can the government really protect consumers from the scourge of unqualified interior decorators? (And does licensing somehow ensure their sense of aesthetics matches yours?)
The downside to all these "consumer protections" is, of course, that consumers are getting screwed by higher costs and lower availability. This benefits license holders in the short term, but in the long term, consumers will find other ways to get their symptoms diagnosed, and their living rooms decorated. In the medical profession, this means that other disciplines are trying to provide the services that increasingly-scarce MDs provided.
An MSNBC article entitled "When the Nurse Wants to be Called 'Doctor'" discusses this phenomenon, and also touches on another side effect — increasing costs to licensees:
For decades, a bachelor's degree was all that was required to become a pharmacist. That changed in 2004 when a doctorate replaced the bachelor's degree as the minimum needed to practice. Physical therapists once needed only bachelor's degrees, too, but the profession will require doctorates of all students by 2015 — the same year that nursing leaders intend to require doctorates of all those becoming nurse practitioners.
More training = fewer qualified practitioners, more student loans to pay off, more money for colleges, higher salary demands, and higher costs to consumers. Remember that the education institutions themselves lobby licensing groups to require more and more credit hours and continuing education — they're the ultimate beneficiaries. And more hours of training offsets higher salary, when you tally up total hours contributed and divide it by total dollars earned.
In the short term, the new education can be of some value, but in the long term, the educational institutions driving these requirements want to provide as little value as possible for as high a cost as can be sustained. For example, insurance agents must have "continuing education" to keep their licenses — a recent poll discovered only 38% of them found such courses even "slightly beneficial, not much" — and only a quarter of agents found them "useful".
So that's the beauty of this scam: in the beginning, greed causes those skilled at some activity (or perhaps not-so-skilled!) to want the government to regulate them. In the end, they themselves end up getting screwed, turning their power over to their union (the AMA is essentially a union, for example) and turning their money over to the universities.