I'm not opposed to doctors but I think most American physicians are horrible at diagnosing and cause a lot of people to end up taking the wrong medications or the medications have a lot of side effects that cause various other issues. My father used to work for the Pharmaceutical industry, and part of staying in business is by getting someone on medication rather than curing the issue.
I still think our surgeons are the best in the world, but in regards to quacks, they are a serious issue. It's true that vitamins help to "prevent" and keep you healthy and even certain fruits and vegetables, but that doesn't guarantee, and once you already have a disease, you really need to see a doctor.