If there's one thing we learn from Fever, 1793 it's that science isn't an exact science. Debates about the cause of the fever and its proper treatment rage through the hospitals and coffeehouses of Philadelphia. There's the school of thought led by Dr. Benjamin Rush (an actual historical figure, by the way) who believes the fever is quickly spreading everywhere and can only be treated by letting blood and administering expectorates. (That means draining the body of fluids and purging with treatments of jalap and calomel. Yikes.) Then there's the French school of thought, practiced by people like Dr. Deveze, who argue that bed rest is the best path to health. Sounds much better to us but hindsight is, as they say, 20/20. We now know that the French were right about things, but what we should really take away from this topic is that science is changing, shifting, and shaping. It's a field of knowledge that's very much a work in progress.
You can't prove everything: even scientific "facts" are sometimes debatable. What we think we know about the world is always changing.
Doctors should do no harm to a patient.