Short answer: Most of them think it will be detrimental to patients and detrimental to the practice of medicine. And various doctors' organizations that have been supportive of ObamaCare are not representative of physicians as a whole.
One noteworthy excerpt:
...America’s doctors know about the scandalous deficiency of access in centralized systems, countries where government’s officials themselves circumvent restrictions when their own personal care is at stake.(Read the full text of "What Do Actual Doctors Think About Obamacare Now?" Link via Dr. Evan Madianos.)
Like when England’s NHS spent more than 1.5 million pounds to pay for thousands of its own staff members to leapfrog their own waiting lists in 2009; or when Italy’s Prime Minister Berlusconi chose to have his heart pacemaker surgery at the Cleveland Clinic in 2006, rather than in Italy; or perhaps when the Canadian Prime Minister of Newfoundland and Labrador, Danny Williams, traveled to the US in 2010 to circumvent Canada’s restrictive system for his own heart valve procedure, because, as he explained, “This was my heart, my choice and my health,” and “I did not sign away my right to get the best possible health care for myself when I entered politics.”
Perhaps America’s doctors see the repeated behind-the-scenes maneuvers by our political leaders in the US, frankly by some of the strongest advocates for more government control of US health care when they or their families are sick.
Like when President Obama, an on-the-record supporter of single- payer systems (“I happen to be a proponent of a single payer universal health care program”on June 30, 2003), was asked pointedly in 2009 to promise that he would not seek out-of-plan help for his wife or daughters if they became sick and the public plan he was then proposing limited their options, the president refused, and instead replied, “If it’s my family member, if it’s my wife, if it’s my children, if it’s my grandmother, I always want them to get the very best care.”
Time and time again, these same outspoken advocates of nationalized health systems for the rest of us, like the late Senator Edward Kennedy of Massachusetts, have exercised their personal freedoms unique to our system for the latest diagnostic tests, the most sophisticated surgical techniques, the most innovative medical therapies, the newest drugs, and the best doctors in the world – right here, in America, where those choices were uniquely available – when confronted with their own personal illnesses.