... a majority of Very Liberal-identifying respondents estimated that >1,000 unarmed black men were killed by police in 2019, with almost a quarter believing it was around 10,000 or higher. In reality, the best estimate is 27 - and if you take the time to read the cases, strikingly few are sympathetic.
However, when presented with evidence that these horrifying beliefs aren't true, people do not feel relief. Instead, they get angry and defensive. They would prefer to live in a world where racist police officers gun down thousands of black civilians every year with impunity. Why would they double down on such an awful lie? Is there any reason beyond peer pressure?
Here's a steelman of this reaction: they recognize you as an enemy with an agenda.
Their picture of reality is not hinging on the particular number of unarmed blacks killed by police, although they find the argumentation around police brutality persuasive and use it frequently. They believe it because they find it to be consilient, coherently integrating many separate observations, logical chains and reliable third-party data; they feel the same way I feel regarding my own beliefs. People are generally similar to each other, and this should be kept in mind.
To skip the prelude. Imagine you're a completely normal, if not very smart person who has the simplest, most cartoonish version of mainstream ideas about Holocaust, which informs much of your opinion on extant and desirable political regimes, geopolitics, art, the moral image of your peers, the historical arc of justice etc etc. Your view is very sane for the most part, but some bits of it aren't. Say, you uncritically, confidently repeat the story of one «Holstein» fellow about Auschwitz masturbation machines – because, really, why wouldn't the evil eugenicist racist Nazis do that after everything else they did? It seems perfectly congruent with the world that you know. And suddenly some obnoxious asshole takes advantage of your error, shows that the story is an embarrassingly stupid fraud, and beats you over the head with it, in public, grinning as he had just deboonked your entire belief system. You defend yourself lamely: «y-you fucking Neo-Nazi bootlicker, I bet you deny the lampshades made of human skin too?» Damn right he does. Bad move, two lives lost. What now? Will you test the fate again?
The correct solution is, in fact, to recognize that you're being led on, that you're out of your depth, and that if you want to keep your beliefs and social role, your best – or at least conservatively least-risky, antifragile – decision for the moment is to stop engaging. Of course you can't do that by dispassionately logging off or walking out, your pride won't allow it. So you've got to insult the crafty opponent in turn, to hope others around turn on him, – and maybe later, in private, do some in-depth research for once, to tell whether your overall model of reality is composed of random lazy hoaxes, or whether it is True and the hoaxes just managed to blend in by imitating the real deal. Maybe they were even seeded by your enemies, to create vulnerabilities which are known in advance – who knows! One thing's for certain: you're not going to discuss this with the smug know-it-all bastard who's plainly using his «Ackchyually» routine in bad faith.
A thousand unarmed black people killed in a year, or only 27 of them? That's a big difference. But there's something like half a million black adults locked up in prison, at a rate of incarceration near sixfold higher than for whites: this difference is massive too. Then there's the stop-and-frisk and broken windows policing, the rate of violent arrests and trauma, there's implicit bias, and structural racism, and stereotype threat, and redlining, and school funding, and housing that preserves segregation, and lead, and that study about rejection rate depending on names on the resumes, KKK, Emmett Till, and don't forget about... So many things, all pointing in one direction. They can't all be wrong. Even if many are, certainly this conspicuous unity means something; there must be some other True facts you're just not educated about. And given how immoral your enemies must be, with their self-evident hostility to universal human values that your tribe and party stands for, what's the Bayesian prior for them honestly bringing up a statistic that ostensibly disproves some particular part of the picture? Even if the particular statistic were to end up true, does this justify providing an injection point for their agenda?
Arguments really are soldiers. You don't have to be mindkilled about politics: it's enough to presume that your enemies are mounting an attack, because this actually happens all the time.