conversation has highlighted that the reason some people object to the term 'mental illness' is because they think the term implies biological abnormality. I don't think this is necessarily the case.
Relating symptoms to their underlying physical pathology was a major advance for medicine from the first half of the nineteenth century (see previous post). We've always needed ways to understand illness even before the development of modern pathology (see another previous post). For example, for many years humoral theory was a model for the working of the body. Both mental and physical illness were understood as an imbalance of the four humors. Such a theory was intended to help make sense of symptoms for people and provide a rationale for doctors’ interventions. Assuming mental illness is a brain abnormality can do exactly the same for modern patients and psychiatrists.
However, I agree with the critics of the term 'mental illness' that there is a gap between the reality and apparent ideal of psychiatry as a physical science (see eg. previous post). The trouble is that we can't understand functional mental illness in physical terms. More generally, we can't understand life in terms of merely mechanical principles of nature. So for example, mental illness can't be reduced to brain disease. I can understand why people don't want to use the term 'mental illness' if it implies brain disease, because to do so is misleading people by making claims that we have biological understanding that we do not.
But, the term 'illness' has always been used wider than our modern definition of physical disease. Technically a distinction has been made in the scientific literature (see my Lancet Psychiatry letter) between illness, which is the personal experience of symptoms and suffering, whereas disease is the underlying biological pathology. Disease is something an organ has; illness is something a person has.
In this sense, mental illness is a perfectly valid concept. I've no objection to using the term 'mental health problems' instead of 'mental illness'. But, functional psychosis, for example, can be seen as an illness. By attempting to reclaim the term 'illness' for such mentally abnormal presentations, I'm not doing so to imply that I think there is an underlying biological disorder for psychosis (see previous post). I don't! But because people do seem to think the term 'mental illness' implies biological abnormality, there is room for confusion. I'm just trying to help clarify what I mean.