" If you identify very strongly with a particular set of qualities in your own nature, then when the opposite surfaces or appears in someone else, then the result is often repugnance. It's frequently a deep moral repugnance, a real distaste of what that other person stands for. It isn't just a casual disinterest or dislike. The shadow arouses anger far out of proportion to the situation. You don't just ignore the fanatic with the leaflets on the street corner. You want to beat in his head.
Why should there be this kind of anger and repulsion? If you penetrate at all deeply into the feelings around a confrontation with the shadow, you will see that the shadow is experienced as a terrible threat. It is a kind of death to allow the shadow any recognition or acceptance. If you are prepared to permit even an inch of tolerance or compassion or value, then the whole edifice of the ego is threatened. Of course the more rigid and entrenched you are in particular attitudes and a particular self-image, the more threatening the shadow becomes. "

― Liz Greene , Meeting the Shadow: The Hidden Power of the Dark Side of Human Nature