Just a taste, really.
It highlights the insidiousness of racism and just how easy it is to stumble into. Granted, not all of these people are racist; some of them are privileged white people. They don't hate black people: they don't expect black people exist.
But of course, non-whites do belong. They aren't unusual or weird. Skin color is just another variation on a theme, like hair color or height. What is different is the social context: if people who aren't white are never encountered in society or portrayed in the media as people first and their race second (or lower. If at all.), then whites will only ever see them as that color. They will never see peers as peers. They will never see people that they could love and be happy with as people they could love and be happy with. They will not even see innocent children as innocent children, marking them as guilty since birth just because of their color.
Wait. That last one.