Fear of "mental" pts
If you mean why do people fear mental patients, there are all kinds of reasons -- mostly based in fear and ignorance.
Mental illness has been stigmatized for generations. Seeing behavior which seems socially "odd" makes many people shy away, rather than try to understand. Also some mental illnesses people to their own need for help -- making it worse. Nami http://www.Nami.Org/ educates ; helps.