Is there a difference between people who naively believe a clear biological cause will be found and those who believe there is a biological cause (even if it can't be found)?
yes, the latter are particularly dangerous because they are indulging in faith rather than science. believing something to be the case even if no evidence can ever been found is the very definition of anti-science
And is the suggestion that if a biological cause can be found for all mental illness, that psychiatry will cease to exist? Does that make psychiatry sort of a field of syndromes rather than illnesses?
The biological psychiatrists will say it's nonsense that if a brain disease is found to cause a mental illness then that mental illness will fall under the province of neurology, but that is historically what has happened. The reality is that psychiatry is not going anywhere despite claims of its death as far back as the 1970s. I think it is a minority position within the field to believe that all problems psychiatrists see are brain diseases. I think most people accept that some of the problems we deal with are clearly due to brain disease (for example someone with vascular dementia who is paranoid that people are stealing from them or someone with traumatic brain injury with affect dysregulation), others are behaviors (for example phobias, addictions), some problems are simply due to sh*tty life cirumstances, other problems are clearly related to life events (bereavement reactions, adjustment disorders) or trauma (PTSD), and many problems are a confluence of factors including randomness, biology, and psychosocial factors (like borderline personality disorder). There is good reason to think that a small proportion of what we call "schizophrenia" is actually genetic disease, a very small number of cases of what we have called "bipolar disorder" are inherited in a mendelian way, and many cases of psychosis are primarily related to environmental factors (both biological like meth or cannabis use or viral infections, and social factors likely deprivation, inequality, racial discrimination).
Some people will argue that major depression is brain disease, which is different to people with sh*tty lives, but I fail to see how the two can be separated in practice.
And is there a suggestion that some mental illnesses don't have a biological component? That's the part I can never get my head around (and why I have trouble understanding what a mental illness is). If it's not of the body, what is it of? It makes it sound very much in the ether.
Well since we can theoretically reduce all human experience and consciousness to neural activity, of course mental illness has a biological component, but no more than any other facet of human experience. The issue comes down to the level of explanation that provides a good explanation for what is going on and provides a way of intervening. I usually teach this as the "levels of explanation" model that presumes we can view all mental disorders at multiple levels, but in a given case one level may be more preferable.
The levels are:
- descriptive (simply describing the problems)
- neurobiological (considering the problem as a result of brain dysfunction)
- psychodynamic (considering the problem as due to intrapsychical conflicts, developmental arrests, interpersonal relationships, and internalized objects)
- cognitive (considering the problem as due to information processing errors or failure or metacognitive monitoring)
- behavioral (considering the problem as due to maladaptive learned behaviors)
- systemic (considering the problem as due to dysfunction in a system such as a couple, family, or organization rather than the individual)
- social realist (considering the problem as shaped by wider social factors such as deprivation, inequality, poverty, discrimination etc)
- social constructivist (considering the problem as a social construction, a problem of narrative)
Of course we can trace emotions and thinking to the brain, but I am entirely unconvinced that this is the most appropriate way of conceptualizing psychiatric problems in the majority of cases. This is not ignoring a biological basis to mental illness, but rejecting neuroessentialist narratives which have held back progress in the field by stifling more pragmatic research and innovations, providing moral exculpation for bad behavior, disempowering people, and leading the mass drugging of the population with psychotropics that they do not need for sociopolitical reasons.
Edit: one of my interests is in how psychiatrists conceptualize different kinds of problems and the widescale implications of this, particularly in terms of criminal responsibility. And you will see that for the most part psychiatrists cannot even agree on what is and isn't mental illness except for a very few diagnostic labels, and they cannot agree on how much biological, social, psychological factors play in different kinds of disorders. but we do know that psychiatrists who primarily see their patients as having brain diseases tend to treat their patients more poorly, and are less likely to include their patients in treatment decisions and are less empathic.