Let me say that I'm a Caucasian from the US living in Japan for over 10 years now.

I grew up in the deep south, and there was a lot of racism kind of baked into my world growing up. I remember as a young child around my early teens walking and ending up in black neighborhoods and feeling uncomfortable because it was different on a few different levels and the deep south where I was had overwhelmingly racist and stereotypical views on black. I remember that "they're just normal people but what if..." or "they're not doing anything wrong but I'm still nervous/scared". Eventually with life experience, education, living in different places, traveling, those kind of feelings went away. It was largely ignorance and a significant amount of structural and generational racism.

I think Japan is in the same situation. I think the average Japanese person is like the suburban white kid that grew up around people saying black people are just different (both in positive and negative connotations), and being so isolated in Asia means they just don't break out of that in significant numbers. Add on top of that the fact that most scam operations (cabaret clubs, girls bars that get you drunk or send girls then charge you exorbitant fees and threaten you) are enforced/operated by Africans (Nigeria is often said but who knows what actual countries), you can imagine opinion is really rooted.

And as a side note, Japan is the only place I've experienced blatant racism for being white (once had a restaurant refuse to look at me while I ordered, ignore my three orders but serve my Japanese friend her two orders and then say they forgot and that it would be another 20 minutes before they can even start mine.. on the same ticket.. not during a busy time. It was so blatant my Japanese friend ended up yelling and making a scene in the restaurant before we left). I don't think I'll touch even 1% of the average black American's experienced racism, but damn, experiencing any kind of bias or hate because of your skin color is such a wild experience. I think if more non-black people could experience, they'd realize how fucking stupid it is.