Monoochrom said:
Bob: It's totally ok to just turn the Tables on racism, it's ok for a black guy to play a white role, the other way however is inacceptable and you are a bad person for thinking any different. My justification? we don't live in a perfect world (so why even bother trying to be fair to everyone)!
The way I remember it, the point was this.
Bob: It's a very good thing for a black person to play a white role, but unacceptable for a white person to play a black role. Why? Because white people have a surplus of role models to draw from in fiction while blacks, asians, and other "non-whites" have a comparatively minuscule number of fictional role models. Having someone of color play a white character is barely a scratch in the number of white role models out there but is a huge addition to the population of black role models. Conversely, white people are not so in need of roles that a white person needs to play a colored role, but having that role taken away from black people is a very big deal because there aren't nearly as many black roles to start with.
He explained it very well, and I'm probably bastardizing his explanation a bit, re-watch the Big Picture episode he mentioned this in if you want the exact wording, but I don't see how he could be misunderstood except by people who actively want there to be significantly more white roles than other racial roles out there.
As for the "not a perfect world" statement, that was in reference to the fact that in a perfect world, we wouldn't care about race in the first place and thus, statistically, every race would have about the same number of roles. But we don't live in this perfect world and whites dominate the fictional landscape, so replacing a white man with someone of a different race is a significant, if minor, step forward, while replacing someone of another race with a white person is a major step backward.