I think one problem here is that an individual scientist/doctor/researcher doesn't actually have to be corrupt to be a shill for the drug companies. They only have to have drunk the kool-aid, and there's plenty of kool-aid to go around. Is it wrong to take money from Coca-Cola if you believe it's total calorie intake, rather than some special effect of refined sugars, that does the damage? It might not be very smart to hold that opinion, but is it unethical?