The definition of disorder:
a disruption of normal physical or mental functions; a disease or abnormal condition.
plural noun: disorders
"eating disorders"
synonyms: disease, infection, complaint, condition, affliction, malady, sickness, illness, ailment, infirmity, irregularity
"a blood disorder"

Even the dictionary understands that mental illness is no different than physical illness. Why is it so hard for the rest of world to see that, I don't know