Reaching WAAAAAAY back to my Abnormal Psyche elective...
There are 25(-ish) major symptoms of schizophrenia. I exhibit most of them. I'd suspect that you do, too.
Most of them are utterly harmless, like "You walk into a room and can't remember why you're there." or "Talking to yourself." (Both of which happen to me all the time, BTW.)
No voices in my as of yet though. I'll keep an ear out.
Bottom Line? There surely is a need for psychologists, some people can cope with their issues better than others (for instance, if I can't remember why I got up and went into a room, if I go back to what I was doing.....it always comes back to me instantly), but other people need help.
As for psyche profs, remember that those who can't do, teach. And for those who write books on the subject.... those who can't teach, pontificate.
those “proofs” of schizophrenia are terribly broad — as you say, nearly everyone could therefore be labelled schizo.