Science vs fiction. Real doctors depend upon scientific studies and compilation of results to determine the best course of therapy. Chiropractors utilize a seriously outmoded, and discredited theory of disease causation to make their statements. What they offer is a sometimes comforting deep massage but no real diagnosis and cure. They are impervious to scientific evidence.
They shouldn't . "alternative" is different than modern western medicine. Generally any drug, herb, treatment, or procedure that stands up to rigorous scientific scrutiny is included in modern medicine. The problem is that many alternative practices, like chiro. Do not stand up to scientific scrutiny and cannot be shown to work. Some patients believe (anecdotally) it works for pain. If really sick, see a doctor.