Sometimes I wonder if some posters just wish to scare every lurking active JW back to the kingdom hall.
And yes, organized religion/belief per se is not classified as delusional in psychiatry...a patient have to have more severe symtoms that belief to be classified as delutional, e g hearing gods voice or acting out their belief in a strange/atypical way. I don't think the people in Al Qaeda or ISIS would primally will be classified as delutional in the traditional psychiatric sence. In some way they are acting rational in their system of belief. And they don't have any (other)symtoms of psychosis/delution.