The Mishnah (Kiddushim 82a) quotes Rebbi Yehudah in the name of Aba Gurya who says that "the best of the doctors [will go] to Gehinom, and the most fit of the slaughterers are the partners of Amalek."
If doctors are given permission to heal, why are they destined for Gehinom?
(1) The doctors eat well and are not humble before G-d; at times they make fatal mistakes; and at times refrain from healing the poor (Rashi).
(2) The primary concern of a doctor is an occupational hazard; a doctor, because of his important role, may tend to become arrogant and conceited and begin to believe that his opinions are truth and that he is perfect and makes no mistakes. Consequently, he might perform treatments which are unnecessary, misdiagnose a patient, or treat him with contraindicative medication. He might feel that he does not have to consult others, or that he does not have to commit the necessary time and thoughtfulness to each patient's condition, due to his years of experience and professionalism. If a doctor views himself with such self-importance, he will cease to be a source of Chesed and, on the contrary, endanger the lives of others. It is the "best" ("Tov") of the doctors -- the ones who are the most successful at their jobs -- who must be the most cautious in order to avoid falling into such a mindset. (Rabbi Akiva Eiger)
(3) The word טוב has a Gematria of 17. The doctor may daven the Shmoneh Ezra (18 blessings) but only really say 17 blessings, since the doctor may believe that matters of healing are in their hands and not in the hands of HaShem (therefore not really saying the blessing of “Heal us”) (Pardes Yosef)
(4) At times a doctor is required to amputate limbs or introduce other medications that are harmful to one part of the body but saves the person. However, if the doctor is “good” and merciful and does not wish to take a “cruel” approach, then refraining from harm to the patient at times leads to the death of the patient and the doctor stands as destined for Gehinom. (Ben Yehoida)
(5) When a person goes to a doctor to heal a disorder, if all goes well, fine. If however, his condition deteriorates he often seeks numerous other opinions. The other doctors always ask for a complete report of the first doctor's findings. Even if they disagree with either his diagnosis or course of treatment, they are very reluctant to say that he was totally wrong, as they in the future will likewise be on the receiving end of a "second and third opinion." This can even lead to the death of the ill person. Their saying "good" to the diagnosis/treatment of the first doctor makes them deserving of Gehinom.
