We expect there to be truth in fiction. Even if you're watching a film like Finding Nemo, where the events obviously never did or could occur, you expect to see realistic relations between characters, realistic emotions, realistic motivations, etc. We get upset if this doesn't happen. That's why we criticize a film if the characters do weird shit. Frozen is rightfully criticized for having Hans turn evil for literally no reason, and "Of course it's unrealistic, it's fiction" doesn't really appease the audience.
People pick up these cues all the time, often without even really realizing it. How many people watched Rocket Power and walked away thinking that surfers really call people "Shoebies"? How many boys have said something extremely cringeworthy to a girl, just because it worked on TV? On some level, everybody knows this. That's why "I'm a comedian" didn't bail Jon Stewart out of trouble when he got caught in a lie. People know that we learn from fiction.
So, enter the wonderful world of Netflix subscribers. Due to our socially incoherent society, a lot of these people have no friends and watch a lot of Netflix. For hours and hours every day, they're beaming in propaganda where de facto segregation doesn't really exist, the blacks are smart and witty, personality differences between the races are just little character quirks, and so on. Their homes look like yours, they don't hate white people at all, and the plotline is always such that you're supposed to root for them in all of their endeavors. They're always morally sound and everything is perfect.
This puts idea germs into sheltered white people, sheltered from either being cooped up in their room or from living in an area where they never actually meet nonwhites. These idea germs are immune to criticism because they're promoted as fiction, rather than as messages that say: "This is what diversity is like, goy." Liberals sometimes try to defend their messages as "There are 325 million people, some must be statistically unlikely." The real question though is why this small number is so alive for liberals and the obvious answer is that they have specific counterexamples in mind... fictional ones.
When they say "I haven't noticed blacks being dumb", they're referring to Timmy Turner's friend, AJ. When they say that they don't notice that nonwhites hate white people, they're referring to JD and Turk. It's been a few years since I actually got into a TV show so I couldn't even imagine the POZ that's going on in Black Mirror or other shit. There are millions of white Americans who's only knowledge of race and diversity is what is beamed into their brains five hours a day and paired with the lack of exposure to the real world, this is extremely dangerous. If you haven't already, turn it off.