The people most obsessed with "racial superiority" in my experience have usually been people who fall short aesthetically, physically and mentally. The lack of personal excellence combined with the desire to perceive themselves in a better light seems to result in being drawn to some form of collective association (racial, national, or otherwise) as a substitute for self-improvement and self-reflection.
A few years back, they did a "looks comparison" between political candidates. It was clear who were the racists - and it had nothing to do with skin color.
I also think that it comes down to jealousy. Other groups can have traits that are desirable, but not held. Who wouldn't want to, look better, run faster, jump higher, or think better?