It would result in a severe shortage of doctors. Medicare reimburses doctors for around 20 cents on the dollar (if that). If we expand Medicare to everyone, doctors would probably end up making less than $40K/year.
Perhaps you are unaware the there has been a shortage of doctors in this country for a decade.
Obamacare does nothing to address that, in fact, it explodes it .. Medicare for all Americans / HR 676 / S 703 does.
Medicare supports Graduate Medical Education.
Physicians for a National Health Program has submitted highlights of S703:
Patients go to any doctor or hospital of their choice.
The program is paid for by combining current sources of government health spending into a single fund with modest new taxes amounting to less than what people now pay for insurance premiums and out-of-pocket expenses.
Comprehensive benefits, including coverage for dental, mental health, and prescription drugs.
While federally funded, the program is to be administered by the states.
By eliminating the high overhead and profits of the private, investor-owned insurance industry, along with the burdensome paperwork imposed on physicians, hospitals and other providers, the plan saves at least $400 billion annually – enough money to provide comprehensive, quality care to all.
Community health centers are fully funded, giving the 60 million Americans now living in rural and underserved areas access to care.
To address the critical shortage of primary care physicians and dentists, the bill provides resources for the National Health Service Corps to train an additional 24,000 health professionals.
http://www.healthcare-now.org/whats-single-payer/s-915hr-1200/s-703