I'm assuming you're white, since all minorities, might not agree, but will understand/sympathize why people complain, demand, ask, and work for "diversity". You, and most white people, take for granted that all if not most of the heroes/heroines from comic books, movies, television, etc. are white. But, let's say you grew up in a mixed society dominated by Asians. People who play main and primary roles in the entertainment business are mostly Asians, what you see and read daily are about Asians even though the people around you are mixed. You will find it tiring, unrealistic, and/or uninteresting. Same thing to most minorities, many of them want to read, watch, and hear stories about their heritage, or at least see some representation of their heritage on some stage. It's only natural.
And don't try to deny; hell, many white students in universities complain there are "too many Asians" in their school already, you think they would like to see Asians in all the movies, television, etc?
The point is, when ethnic minorities, see white people playing prominent roles all the time, they ask themselves, "why aren't there people who looks like us." We are tired of seeing the same faces everywhere. It's almost as if they are being ignored, and when they do see someone who looks like them on the stage is usually in demean, and negative light.
White insecurities comes from the fact that Asian Americans are the fastest demography in the U.S. and are in average likely to be better educated and compete with the white population. The sense of "yellow peril" (http://en.wikipedia.org/wiki/Yellow_Peril), stems from this insecurity. American higher education universities such as the Ivy Leagues, FEAR that if they discard the "affirmative action" from their enrollment decisions, Asians would become the dominate demography in student body as it happened in the campuses of University of California, and University of Chicago (http://www.nytimes.com/2014/11/25/opinion/is-harvard-unfair-to-asian-americans.html). Some of the symptoms of this is the fact that whites has to keep on affirming that Asians are not fit for leadership roles compared to whites, Asians are hard working but not creative, etc. Yet, many who contribute to innovation and economic growth are Asians/Asian Americans.
As Louis CK puts it; "I don't want to see the future and find out what happens to white people." (https://www.youtube.com/watch?v=A7FawbAJpoQ). When the field is even and equal where everyone has equal opportunity and representation, whites will lose their status quo, and the threat right now that would undermine that status quo are Asians.