People are reassured by diagnoses
Many people actively want their doctor to give a diagnosis. People are dissatisfied when they do not receive a diagnosis and often describe their 'struggles' in obtaining a diagnosis from an unresponsive system. Giving a name to our distress serves a function and, after all, naming something is an important psychological event. If you are plagued by thoughts of being a terrible parent whose children would be better off without you, hearing that you are 'ill' and that what you are experiencing has a name and can be treated, can be very reassuring. You're not going mad, you're not a bad mother, you're not mistaken ... you're just ill and can be fixed.
When you look in detail at what medical diagnoses do and don't mean, you might wonder why people find them reassuring. Some of course are hugely valid and important. For example, government campaigns urge us to look out for blood in our bowel movements. This is important, because that can be a symptom of bowel cancer. And, to drive the point home, recognising that you have bowel cancer is something that is not merely synonymous with having blood in the toilet, it is entirely the province of medicine, and the diagnosis (of cancer) is clearly more than the symptom (the blood itself). But in mental health, especially, that logic seems to falter. The 'diagnoses' often appear to be nothing more than a very brief repetition of the problems that the person took to the doctor. This happens occasionally in physical health, too. A person may go to a doctor complaining that their hair is falling out and get told that they have 'alopecia'. They may add that they think the hair has started falling out after a period of considerable emotional stress and be told they have 'stress-related alopecia' or perhaps 'alopecia NOS'. The 'NOS' is shorthand for 'not otherwise specified'. The person has gone to their doctor reporting that their hair is falling out, the doctor has translated that into 'alopecia' and - me included - we feel somehow reassured by this. It's perhaps significant that the diagnoses are often in Latin or Greek. The languages of tradition, of academic authority, of antiquity and of the clerics carry a lot of symbolic weight.
In practice, of course, there is more happening here than merely the diagnosis itself. The diagnosis, the tone of voice, the non-verbal behaviours and so on all tell the patient that the doctor has heard and, to a degree, understood their problems. The technical, slightly obscure, language, indicates that the doctor is an expert in the field, and conveys confidence. However, despite these potential or possible benefits, a cool and dispassionate look at the data suggests it may be difficult to make valid, reliable or useful diagnoses of psychological problems.