While think those officers were wrong and deserve to pay the price. I don't agree with Black Lives Matter's core mission "#BlackLivesMatter was founded in 2013 in response to the acquittal of Trayvon Martin’s murderer. Black Lives Matter Foundation, Inc is a global organization in the US, UK, and Canada, whose mission is to eradicate white supremacy and build local power to intervene in violence inflicted on Black communities by the state and vigilantes."
I think Police reform is long overdue, and that extends to accountability even beyond excessive force. However, this notion of wide spread white-on-black murder is not supported by actual data:
https://ucr.fbi.gov/crime-in-the-u.s/2017/crime-in-the-u.s.-2017/topic-pages/tables/expanded-homicide-data-table-6.xls