The best snake oil salesmen believe in their products. There are already exceptions for allowing people to take highly experimental procedures when there likely to die without them. However, there are plenty of cases where highly trained well meaning doctors caused massive suffering without benefit to their direct patents.

As a recent example of fringe medicine, a few athletes have injected themselves with stem cells. Not to mention the modern version of doping which often involves substances that are known to be harmful or medicine has little idea what the long term effects are.