I tend to think people's attitudes come from too much diversity rather than too little.
The most diverse places I've ever been are also the most visibly segregated and racially aware (but not in a good way). Meanwhile, I see the most tolerance for others in homogeneous places.
>>Press2+(OP)
I've observed that racial stereotypes seem to be borne out more often than not in the urban environments I've lived in, because minorities there tend to be disproportionately poor and uneducated. So I share your skepticism that "diversity" per se is the answer to prejudice. Canada for example is much more white on the whole compared to the US, and far more tolerant on the whole. Ditto with Scandinavia etc.