There is much that is unknown in medicine/healthcare. When future generations (with access to ever-increasing amounts of data) look back at what we are doing today, they will no doubt find much of it on par with bloodletting and lobotomies, or PSA tests and coronary stents, often causing more harm than good. Nonetheless, most of us are trying to do the best we can, working with what we currently know, and being open to new evidence, correction, and progress.
An ethical issue arises, however, when this is not acknowledged by doctors to their patients, and treatments/screenings are recommended without adequately informing patients of the chance of benefit, the chance of harm or unwanted treatment cascades, and the state of the evidence (or lack thereof) supporting that assessment. For example, patients should be clearly informed whether a treatment or screening is being recommended on the basis of anecdotes/tradition/observational case studies, or well-designed, blinded randomized controlled trials with adequate sample sizes and long-term morbidity/mortality figures; and they should be informed of the NNT (“number needed to treat”). Failing to disclose the state of the evidence denies patients the opportunity to give truly informed informed consent, which is at the crux of what is exploitative and unethical in healthcare. When a doctor presents a recommendation with more confidence than is warranted by the nature of the evidence, she is betraying the trust of her patient. If the patient is fully informed that a treatment or screening has only weak evidence and chooses to consent anyway, then that is their prerogative. If the patient is not fully informed of the evidence for a treatment or screening, then informed consent is missing. Informed consent is what draws the line between honest service and manipulation, between legal contact and assault, and the ‘informed’ part is not optional. 
 Note: There may be exceptions in time-sensitive, life-threatening emergency rescue situations, but it’s important that these remain exceptional.