Based on the information given, the biggest disadvantage of assigning a diagnosis is that it can be stigmatizing and bring about a negative bias for the client.
For the patient, it should be noted that facing prejudicial attitudes or biases can lead to shame and lowered self-esteem.
A typical stereotype that is associated with those with mental illness is that they're irresponsible and unreliable. Among all the mental illnesses, schizophrenia is most negatively perceived in my view. Such people having it may be more prone to negative biases.
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