They do though. Your personality, culture and appearance are the main components of how people perceive you, your identity. The main thing you can associate with bad behaviour is domestic culture. It's not racist to say that African Americans have below-average educational attainment and above-average criminality. This is as contrasted to African immigrants to America who are quite opposite. These groups are equally "black". It therefore also isn't racist to pre-judge African Americans based on this information. I suspect most "racism" in the US is along these lines, and is correlated by the experience of my foreign-born black friends. They find that Americans who treated them with hostility do a 180 when they open their mouths and speak with a British or African accent. You also don't have to look far in the African immigrant community to find total hostility to American black culture.
> generate 100 short descriptions of families for a project
There's no reason this can't be interpreted as generating 100 variations of the mean family. Why do you think that every sample has to be implicitly representative of the US population?