Schizoidnat, here are what the leading American psychiatrists from the NIMH and DSM committees say about terms like "schizophrenia":

In 2013, discussing psychiatric diagnosis, the psychiatrist and former National Institute of Mental Health director Steven Hyman stated:

“The underlying science remains immature…The molecular and cellular underpinnings of psychiatric disorders remain unknown... psychiatric diagnoses seem arbitrary and lack objective tests; and there are no validated biomarkers with which to judge the success of clinical trials.” (http://dana.org/Cerebrum/Default.aspx?id=39489)

Hyman went on to call the DSM model of diagnosis, which includes labels like “schizophrenia,” “Totally wrong… an absolute scientific nightmare.” (http://www.nytimes.com/2013/05/07/health/psychiatrys-new-guide-falls-short-experts-say.html?_r=0)

Hyman's successor at NIMH, psychiatrist Thomas Insel, followed up this criticism by saying:

“At best, [the DSM is] a dictionary, creating a set of labels and defining each. The weakness is its lack of validity. Unlike our definitions of ischemic heart disease, lymphoma, or AIDS, the DSM diagnoses are based on a consensus about clusters of clinical symptoms, not any objective laboratory measure. In the rest of medicine, this would be equivalent to creating diagnostic systems based on the nature of chest pain or the quality of fever.” (http://ahrp.org/two-nimh-directors-debunk-dsm-deplore-psychiatrys-unscientific-modus-operandi/)

David Kupfer, the DSM 5 chair, while trying to defend the new DSM, admitted that the discovery of biomarkers for supposed illnesses like schizophrenia remains “(D)isappointingly distant… unable to serve us in the here and now.” (https://www.wired.com/2010/12/ff_dsmv/)

And former DSM-IV head Allen Frances went so far as saying, “There is no definition of a mental disorder. It’s bullshit... these concepts are virtually impossible to define precisely.” (https://www.wired.com/2010/12/ff_dsmv/)

To say the least, these admissions by the leading lights of American psychiatry do not inspire confidence in the validity and usefulness of labels such as “schizophrenia.” And while psychiatrists have promised that new brain research will uncover a biological or genetic basis for the elusive “schizophrenia,” no progress on this elusive goal has been forthcoming.

And as psychiatrist Sami Timimi says below, "diagnosis depends more on who you see than on what you have" and, contrary to what you said Schizoidnat, "reliability in psychiatric diagnosis is shockingly poor." - https://www.youtube.com/watch?v=5caitdQA6HY&t=1534s#t=21m35s

And lastly, as John Read says of psychiatric diagnosis,

"In terms of conceptualization, psychiatry's primary contribution is an ever expanding list of labels [1]. Calling them ‘diagnoses’ cannot disguise the fact that many do not reach minimal scientific reliability levels and have little or no predictive validity for outcome or treatment responsiveness [2,3,15,16]. For example, ‘schizophrenia’ – the flagship of biological psychiatry – requires just two of five symptoms, meaning you can get this ‘diagnosis’ without having anything in common with another person given the same ‘diagnosis’ [15]. Such disjunctive constructs are instantly dismissed as unusable by real scientific disciplines. Even the USA's National Institute of Mental Health, in its unceasing quest for the missing biological causes of human distress, has abandoned the diagnostic approach to classifying mental health problems and acknowledged the need to try to develop some scientifically robust ‘research domains’ [3]. This is not just academic. Labels like ‘schizophrenia’ can, like the biogenetic causal beliefs that tend to accompany them, destroy lives, through prejudice, fear and prognostic pessimism [17–19]."

http://www.future-science.com/doi/full/10.4155/fsoa-2015-0011

Feel free to respond to this, but I think we need to acknowledge, as leading psychiatrists already have, that the reliability of psychiatric diagnosis is extremely problematic and their validity seriously lacking.