There are varying degrees of narcissistic personality disorders. Most commonly these people seem to be scared and grossed out by anything they do not deem as normal, from political view points, to skin colors, to sexuality. They refuse to accept anything but their identified norms as being right, and everyone else is varying degrees of abomination to them.
So we pretty much already know why people like this behave the way they do towards people they don't deem as normal.