Please explain what do you think causes the stigma attached to mental illness?

Good question!: It may have started when abnormal behavior was thought due to demonic possession . The sufferer was "evil." it also may stem from the falsehood that mental illness is a choice, i.e., to avoid responsibility or be lazy. Most important, i think, is fear due to its mystery — the fear that none of us are that far from insanity, so we defensively stigmatize the mentally ill to feel safe ourselves.