There has been a lot of controversy created over the years regarding the supposed issue of diagnosis. The controversy seems to have grown more acute since SCASA received recognition from the U.S. Secretary of Education, in essence, an event which signaled a federal government distinction between the two schools of thought within the chiropractic profession nationwide.
Before we can talk clearly about this "issue," it is necessary to understand what is meant by the term diagnosis. According to Dorland's Medical Dictionary, it is "the art of distinguishing one disease from another." Based on this, if you need to know what disease a patient has you need to practice diagnosis. It is obviously part of the medical doctor's practice; medicine is the treatment of disease. For chiropractic, though, I believe there will be three representative reactions from among the groups within the profession.
The liberal mixer (i.e., the mixer group which views chiropractic as unlimited primary health care -- unlimited as to anatomy addressed, conditions treated, or methods used, though most laws state it as a limited profession) would feel that diagnosis is a necessary part of his practice. It seems logical for him to feel this way. After all, with the goal of treating diseases, it is important to know what disease the patient has so that a treatment of choice can be decided and provided. He must, as an example, know if the patient has a headache in order to decide what type of drug or therapy (subject to the limits of the law) to use to treat it. He could not responsibly reach such a decision otherwise. Without making a diagnosis, the liberal mixer could not practice.
The conservative mixer (i.e., the mixer group which views chiropractic as limited primary health care -- limited in one or more of the areas of anatomy addressed, conditions treated or methods used; for example, some conservative mixers are spine-only doctors, some treat only musculoskeletal conditions, some use only manipulative therapies, etc. There is quite a bit of latitude as to what the limitations may be, though there seems to be a nearly unanimous feeling among conservative mixers that they shun the use of drugs and surgery as treatment methods) would also feel that diagnosis is a necessary part of his practice. Again, with the goal of treating diseases, even if only some of them, it is important to know what disease the patient has. In this case, though, it's necessary to know this, not only for deciding what type of treatment to use but also to know if it's one of the "non-chiropractic" diseases. The conservative mixer, then, needs to know if the patient is suffering from, for example, one of the 8, 10 or 12 "danger signals" or if it's something else that he doesn't treat.
The straight (i.e., the straight group which views chiropractic as limited primary health care -- limited to the anatomy of the spine, the condition of vertebral subluxation, and the method of chiropractic adjustment) would feel that diagnosis is not a necessary part of his practice. Remember that diagnosis is distinguishing diseases. Unless we reclassify vertebral subluxation as a disease, which it's not, diagnosis is not something a straight chiropractor needs to perform to meet his objective of contributing to a person's health by correcting vertebral subluxations. Determining subluxations does not require a disease diagnosis.
The issue, then, of whether to diagnose or not is not terribly controversial at all; if you mix, you need to diagnose, if you practice straight, you don't. The controversy arises when one group tries to force its decision on the other. Deciding to make a diagnosis should be controlled by what your care objective is. If you are treating disease, it is a must. If you are not treating disease, making a diagnosis is wasteful and potentially harmful. If straights didn't bother themselves with the mixers' decision to diagnose and if the mixers didn't bother themselves with the straights' decision not to diagnose, and if -- an important one -- they lobbied, either independently or together, consistently to have the rights of both to make their own choices on this and other concerns, then there would be no "diagnosis issue" or other controversies.