This isn't a black problem so much as an asset turned liability in human nature. Bruce Schneier wrote about it before where people are more likely to believe anecdotes, especially scary ones (eg worst-case scenarios), from their peers than objective data collected from either peers or other side. The hypothesis at the time was that its a trait that helped early humans survive against threats that killed them (esp ate them). The people that listened to a story about what came before a death (eg animal attack) might survive more often than those who dispassionately collected and analyzed data before committing to something. Over time, the ones that were left were more likely to believe what the group was telling them focused on the same risks, esp extreme ones that rarely happen but result in death.
So, that's what the BLM folks were doing. The people they identify with were making these claims. They supported them using far-away examples like Ferguson and Baltimore. They believed them going with the flow. It's the same effect behind the many Trump voters out here worried everyone that's Middle Eastern might be a terrorist that might take lives. Although, they do hardly anything like better diets or extra vigilance behind the wheel to avoid the leading causes of death of Americans. They're also not looking at every right-wing, patriotic person despite such people committing acts of terrorism in the past or collecting lots of guns planning for... something. Jump on and defend anything from in-group while excluding, perverting, or reflexively dismissing out-group.
Human nature I'm afraid. Everyone doing this needs to learn to knock it off since it just makes us fight for nothing. More important, we miss opportunities to discuss what's really going on to improve our circumstances. The BLM people's BS is easily called out with the middle and right-leaning folks reacting as "You can't trust any of this stuff. People just bullshiting for attention to their causes." We can't stop racism creating reactions like that. Sadly and unfairly, we have to be better than most people in accuracy making sure we consistently build our interpretations on solid data with no misdirections or lies. Especially selective stuff. Consistently good use of data, civil interpretations, and pre-packaged solutions are the right combo to get more people onboard fixing things. Fortunately, there's quite a few of us down here trying to do that with many more just trying to get along despite our differences. The peaceful results of the I-40 protest in a often-racist, often-murderous area confirm how well we do this I think. We were all so worried shit would happen but it didn't. (slow, long sigh of relief)
I don't claim any particular knowledge of what's wrong with the police anywhere, but when cops or people who identify with them say reflexively "well, we'll just stop defending you from the thugs if you don't like us" my gut tells me that it means they already were deliberately enabling "thugs"; the declamation sounds like something that people have repeated to themselves for years, bottled up the justification for corruption and the protests just give permission to let it out.