I have an irrational fear of heights. I know why I have it, I know what triggers it, and I have learned to control it. I was a pole vaulter in my past life and I jump out of airplanes from time to time in my profession. I am still scared and have to work very hard to prepare myself to do these things.
I do agree, that much fear comes from not knowing (ignorance) I do think this is the most dangerous type of fear.
Maybe there is a difference between fear and phobias???
I take my PT test every six months, I have never ever failed, and never will, however I still get nervous every time simply because I am being tested. It too is an irrational fear.