"Mental illness" is largely a matter of who's doing the defining. During the heyday of Communism anyone who didn't toe the Party line could easily find himself in a "mental health hospital." The dominant group usually has the power of confinement over any anti-establishment figure who crosses normative boundaries.
Certainly there are genuine psychotics and neurotics who pose hazards to themselves and others. That's real mental illness. But outfits like the American Pyschological Association have entered the field of politics and pose a huge danger, redefining mental illness along politically correct lines; as do the type of social workers who brought us terrifying travesties such as the McMartin Preschool disaster. This is very scary stuff.