Fair enough, but that perception still has to be tied to race (biological differences), otherwise it wouldn't be racism. An Australian Christian of middle-Eastern descent, for example, seems more likely to encounter racial prejudice in Australia than a white Muslim (correct me if I'm wrong!)... while the prejudice is based on cultural differences, those differences don't necessarily exist. They're just part of a package which associates "middle-Eastern" with "Muslim" (and "Arab"). The assumption that everyone of a particular race is of a particular culture is what links a sense of cultural superiority to racism.

Just to clarify, that isn't to say that prejudice against people of other cultures is okay. The assumption that everyone of a given culture has the same views and opinions is prejudice: assuming you know something about a person given no evidence. Once you have evidence that an individual supports ideas or actions that you consider ethically (or, I guess, morally) wrong, it's no longer prejudice; it's just a judgement.