>they do know HUGELY more about medicine, disease, interventions, symptoms and so forth than you do (and almost certainly more than you will ever know).

Depends. When it comes you many chronic conditions (example: high cholesterol), their treatments will actively harm you, than when left untreated. There are a lot of bogus treatments out there and certainly they will appear to know a lot, but it's harmful intervention that they know.

Bottom line - you have to take a call depending on the situation. As a general rule complete disregard for authority in case of medicine in a developed country will do more people OVERALL good. I'm not saying that they cannot be legitimately helpful, but those cases are far and few in the developed world.