Why do non-Caucasian people smell so bad to you?

It could just be your perceptions. Members of various groups do smell differently due to genes, predominant occupation, and diet. Poverty, poor hygiene, and sickness can make anyone smell bad, regardless of race.

You might not notice people who smell like you, since you are desensitized to it. People who live on farms do not constantly perceive the odor of manure. They smell it all the time and have learned to ignore it. But they might notice another strong odor. Imagine someone being on a farm around a lot of manure and complaining about the odor of someone's cigarette. So perception of body odor works the same way.