Every single person I worked with in Rocky Mount had spoken with Black people and worked with Black people. They lived on the same streets and their kids went to the same schools. And many of those white people who interacted with Black people every day were stunningly racist (and I should say many weren't). Maybe they categorized "different types" of black people. But they could hold a civil conversation, then turn around and stereotype, or drop the n-word repeatedly.
Your vision of what people have been exposed to is a cartoon.
"In fact, PRRI's data show that a full 75 percent of whites have "entirely white social networks without any minority presence." The same holds true for slightly less than two-thirds of black Americans." Now isolate the 14% black population from all minorities, take into account how minorities cluster and the 75% number is for black friendship is probably even higher than 90%
I think those are not updated, but using a more restrictive methodology. And while it's not invalid, I think the statistic I cite is more relevant. For your initial question, who have you talked to, the acquaintances at work are more important than confidants.
Like I said in my original post, you're asking a good question. As far as I understand it, most people's stereotypes are not based on significant interaction with other people. They're picked up from other people who held those stereotypes.
It's just that I think you made a major exaggeration going along with it.
The sad truth I've heard people who were racist as hell say "they're just blaming that boy because he's black." They were capable of seeing someone as human in a particular instant, then turning around and uttering the most hateful things imaginable. They could talk to a black man civilly then turn around and talk about what "the brothers" do. Not having talked to black people wasn't their problem.
At a guess, 80% of the white people I know. I live in Washington, DC, where you would have to go out of your way not to have black co-workers. Yet I had black teachers and classmates in high school in Denver long ago.
All the white people I know (since knowing people takes "actual interaction") have spoken to a black (or, at least, a multiracial person with black enough features to be generally considered "black" by observers) person enough to meet that standard, pretty much by definition.
But, while I think your 90% number is a substantial exaggeration, you do make a good point that this is probably far less common than most people think it is.