So... There's a correlation between lower socioeconomic status and violent crime? I don't think that's surprising. What it does not do is explain why those demographics are overrepresented in either category.
I also am highly skeptical of "every paper", unless you're specifically going out of your way to only read the ones that confirm your bias.
That is what "$GROUP is a bunch of violent thugs" implies: that members of that group are intrinsically more likely to be violent and thuggish than other type of people, specifically because of the trait that $GROUP embodies. That statement does not hold true for black people, but I believe it does for police.
It's important to understand the root causes of things. Black people commit more crimes, because black people are overrepresented when it comes to lower socioeconomic status, because of century-spanning systemic racism and the reduced opportunities that brings.
Police tend to be more violent and thuggish because the profession selects for people who want to have (and inevitably abuse) power over others, and because it's systemically set up as an institution to enable that behavior and not hold members accountable for it.
I would hope from those two descriptions it's reasonable to say that one group's failings come from a sympathetic cause that is often out of their control, and the other group's failings are intentional and by design.
But we cannot say that it's not intrinsic, either! All we can tell is that there's a correlation between "being black" and "being poor". Like the person I was responding to pointed out: there's the potential for a hidden variable that connects these two things. Alternatively, one causes the other. Given the available evidence, it does not seem clear that the arrow of causality points in either direction.
This is the point that you're missing. You assume that "being poor" causes people to be "more violent", when it's equally plausible that being "more violent" causes people to be "more poor".
And if being "more violent" is something that is intrinsic to certain demographic groups, then the latter interpretation would fully explain the overrepresentation in both lower socioeconomic classes and in rates of violent crime.
I fully agree that there has been systemic racism that contributes to lower socioeconomic status for some racial demographics. However, I refuse to accept that as the only explanation for those same demographics being highly overrepresented in violent crime statistics. This is not a simple problem with a two-dimensional answer. The "systemic racism" argument may be necessary, but it is not sufficient, because it attempts to remove any kind of agency those same demographics have over their own behavior, culture, and identity.
This is both wildly disempowering and enabling. You're essentially excusing every individual in that demographic from the consequences of their violent criminal actions by putting the blame entirely outside their control, which is bullshit.