I think I understand what you are saying, and in theory it's right: being prejudiced about people we don't know is wrong, and if the only reason isomeone change his view on race relations is because of entertainers or pop-culture references, it's sad and stupid. But in the real world sadly, it's mostly how it works.
I'm a muslim of Algerian descent who live in France, and I have seen these last twenty years how the rise of Algerian mainstream actors, comics, singers... has changed how we are viewed, even if it doesn't ended racism at all. Like Guy Debord (a french philosopher) said we live in "the society of the spectacle" even if we don't like it. Pop-culture representation will not end racism but it will help a lot: a famous stand-upper who is loved by a large part of the population will do more for race relationships than an academic in the short term. And thats why I liked the X-men run of Morrison: he understood the importance of pop culture and cultural war to win battles. In our modern society, to fight racism you need to win the culture war.