Why have medical school at all then? Why not just let anyone who wants to be a doctor be hired by a hospital and learn as they go?
I don't know? Why not just let anyone who wants to work that way, do it?
Onto your other concerns:
First of all, who knows how you and other employers will find your employees in the future.
Who knows what institutions will produce the best doctors.
My guess is, that in a completely liberalized system, modes of education would emerge, that would be favored by the employers. Now, if you wanna go with the old apprentice model, be my guest. Others might prefer to hire those who have attended med schools, those having passed certification exams in other countries, those having certificates that they have attended physical exam classes, etc.
There would be no quality control. And the USMLE's are not quality control.
Supporting the existing quality control, is like forcing everybody to pay for the same insurance. The consequences of quality control directly affects the availability of cheap medicine. The forced quality control in the US model, is keeping supply of doctors down, because there are a limited amount of residencies, prog.dirs can be picky, and this keeps the market from being flooded with cheap mexican and east european doctors.
The employers and the patients could very well do quality control, according to what quality control they find worthy of the price tag. It would be up to you to run background checks on new employees, their training, and their fit into your organization.
It is easy to see how new technology can increase transparency, and make it easier for the general public to estimate the quality of the doctors in question, their popularity, their controversies, etc. If you want government-guided control, have the government do a ranking list of doctors and customer health and make it public.
You act on the assumption that we all ought to support a god-given quality control, due to a natural obligation to prevent doctors from seeing patients unless they reach an arbitrarily quantifiable score, and pass a selection based on vague personality criteria during residency. That is just your preference, or your cynical best interests, but has nothing to do with craziness and morality. That is just BS argumentation, and you are intelligent enough to know it.
The honest argument is that current doctors would not benefit from this. Most patients would. Students wanting to become doctors, who can't afford it, would benefit. It is a conflict of interests.