Why is schizophrenia an illness?

its really best that you consult specialist for it.

Because it requires medication to keep it under control.
Because part of the body, the brain, is not functioning as it should. It is potentially harmful to the individual that is afflicted.
Because its not normal to have auditory and visual hallucinations
Schizophrenia is very serious mental disease. It disturbs patients life completely. These patients have hallucinations and delusions. Many years ago as there was no treatment for the disease the patients were suffering whole their life. Many studies has been shown that in the process of this illness brain mediators (chemicals which acts in the brain) are go imbalanced.