Without saying I agree or disagree, if I take the position that racism in policing doesn't exist, and that the police are treating everyone equally:
America has in prison today almost 0.7% of its entire population. Right now. It is the world's leading jailer on a per-capita basis. [1] Two thirds of private prisons (which lets step back for a second is horrifying as a concept) include minimum occupancy clauses. [2] This is an utter failure of the state in its duty of care to its citizens. To call this a conflict of interest doesn't even begin to do it justice.
The incarceration rate among African Americans is almost 7X that of white folks in America. Criminality and race do not go hand in hand, therefore there exists a real and meaningful problem that is disproportionately affecting a racial group. A social and/or economic problem.
African Americans have way more interaction with police and policing, and even if you believe there's no racial disparity in the way those interactions go down - that instead they're killed and harassed at the same rate as white folks on a per-encounter basis - the fact is they have way, way more encounters per capita. This is likely a function of the society that America has built and fostered.
The reaction and the frustration and the protest is still justified even if you believe that race didn't play a factor in the specific instances, and even if you believe there's no systemic issue with policing.
Now, there's also evidence that there is a difference in how they are treated by police, but I think my argument holds even if you reject that premise.
[1] https://en.wikipedia.org/wiki/United_States_incarceration_ra....
[2] https://www.prisonlegalnews.org/news/2015/jul/31/report-find...