I understand why some people would consider psychiatry as being in its own category away from most medical sciences. Psychiatry doesn't truly adhere to the medical paradigm, which is the view that the location of symptoms indicate their etiology and are often caused by pathogens of some type, which can be analyzed and subsequently treated. This doesn't apply for psychiatry because regardless of the behaviour, it boils down to some part of the brain, which may interact with other bodily areas (i.e. HPA axis for those who are biologically or medically-inclined).

I consider psychiatry to be a reputable field of medical science but not in the same boat as neurology, cardiology, etc... . For those who deny psychiatry as a legit medical field, they're either incredibly deluded on their high horse or they're running away from the fact they have a mental illness they aren't coming to terms with, so the only person they see as responsible for the "faulty" diagnosis is the psychiatrist.

Coming from someone who studies in the neuro, physiological and medical sciences field, there is a huge amount of knowledge of the brain and its mechanisms, however, there's an equally big if not bigger amount of uncertainty because we just don't know how or why something functions in a particular way. For one of my research courses, I gave a mini-lecture presentation of the molecular and cellular physiology of rapamycin. In preparing for it, I did some background research, found excellent schematics but when people asked certain questions at the end of the presentation, I could only answer with, "the scientific community does not know the answer". This relates to medications because drug companies strive to design a medication that is maximally therapeutic with minimal and few side-effects. There are medications that have (almost) no side-effects but they're few and far in between.