I firmly believe that lack of exposure to people of different cultures or races leads people to be racist and not necessarily realize it. If you’re never around X, how can you know you have an inappropriate reaction to X?
To illustrate this, I didn’t know about my escalator phobia until I moved away for college. I entered the mall, saw these moving stair-things, and felt a deep fear in the pit of my stomach. I hadn’t seen an escalator since I was a toddler and, if you’d asked me on high school, I’d have denied having a phobia.
(I’ve successfully worked on my phobia over the last decade, showing that changing inappropriate reactions is possible)